Most flatbed scanners today come with a transparency adapter that enables the scanning of negatives or transparencies (slides).  Though most flatbed scanners support scanning a negative or transparency, much better results are obtained by using a dedicated film scanner specifically designed for such purposes.  Film scanners typically have a much higher dynamic range than does a flatbed, and the optics and mechanical transports are designed out of necessity to much tighter tolerances. A good film scanner is also quite expensive in comparison to a flatbed.

Answer:  Sadly, the answer is NO...... (not quite what you wanted to hear, right ?).  The 2400 refers to the number of sensors/inch on the sensor array. True, both are capable of resolving 2400 dpi from a theoretical standpoint, but from a practical real world standpoint, the differences may be (read: probably will be) significant.

Just because a scanner has an sensor array of say 2400 dpi, doesn't necessarily mean that it will be able to resolve 2400 lines per inch on a resolution test chart. The sample spot size (each pixel) must be matched to the number of dpi. Sloppy manufacturing techniques and tolerances in the mirror and lens systems can often result in an excessively large sample spot size, such that there is greater than 10% overlap of adjacent samples.  50% overlap for example, would result in actually something less than 1200 resolvable lines per inch. Thus the 2400 dpi spec for practical purposes might be completely bogus.  True, it will sample 2400 dpi, but might not be able to resolve anywhere's near 2400 dpi !

Also, like a camera, the image must be held steady while the image is being exposed (or scanned in this case). Any movement, and worse case, you'll get a "perfectly exposed blur" ...or variations thereof.  A well constructed commercial grade scanner employs highly accurate, smooth stepping motors housed in a heavy rigid cast frame with good isolation dampening.  The $99.95 special you can safely bet, will be constructed out of "Genuine Re-cycled lightweight Plastic"  throughout. The entire unit shakes, hums and vibrates as the image is being scanned.  Even if the scanner has the best CCD array and optics, it will be all for naught if they are housed in a glorified cement mixer.

Also critical is the back focus.  Cheapie scanners are factory set to focus on the media side of the platen. One setting does all, but it is susceptible to getting knocked out of whack  (plastic isn't all that structurally sound a material ).  Better scanners use a computer controlled focusing motor that optimizes the back focus for each print scanned.

Optics are also a critical component.... Keep in mind that most scanners have a "sweet spot" where the highest resolvable number of lines is obtained. It is usually (though not always) a 4 x 5 inch area in the center of the platten or often times a relatively narrow strip down the middle, depending upon the optics design. Lens aberrations as well as astigmatism result in softening of images at the edges.  It is for this reason that transparencies are to be scanned in the sweet spot. Keep in mind that some manufacturer's rate the resolution of their product only in this "golden spot"... Anything outside this sweet spot will probably yield results substantially less than gloriously claimed and touted.  Note that inexpensive scanners employ "genuine" plastic lenses. A plastic lens is no match for a high quality coated 5 or 8 element glass lens - the glass lens itself costing more than the price of the entire cheapie scanner alone.  Naturally, all this is a lot more expensive to manufacture.

A penetrating glimpse of the obvious perhaps, but It's a pretty safe bet that an inexpensive scanner will have poor real world dynamic range. (2.7 or lower).

Alas, you tend to get what you pay for. Something to consider is that the bargain scanners will soon be outdated, whereas a quality device will typically have 2 to 3 times the life before newer technology makes them obsolete. Thus in true dollar costs averaged over it's life, a better grade scanner may actually be cheaper or maybe be only marginally more expensive in the long run. In general, it's recommended to purchase the best scanner to match your highest level of anticipated use. Keep in mind that If all you need is a small pickup truck, there's no need in purchasing a Kenworth W-900 Condo Cab with a 600 HP CAT Turbo Diesel hooked to a 53 ft trailer.  Thus for non-critical general scanning and personal email use, the $39.95 to $99.95 special will probably be just fine. Keep in mind that less than 20 years ago, a scanner offering the capabilities of the $99.95 special of today, cost then close to $10,000.

TWAIN is a software protocol that serves as a link between the application you are running to import the image and the scanner. The TWAIN protocol is thus a standard to which the device driver is written and has been agreed on by the software as well as hardware manufacturers.  Almost all applications are TWAIN compliant, and just about all scanner manufacturers' write their device drivers to be TWAIN compliant as well.  TWAIN allows whatever application you are running to recognize the scanner and effect communication with the device.  When you see advertising that states "TWAIN Compliant", it means that the device driver for the scanner (or other imaging device) is exactly that.

Purchasing a professional grade scanner makes no sense if your only intended use is for scanning snapshots to be included in emails to Grandma. In that case, even the $39.95 scanner will probably suffice.

Most scanners in the $150 to $250 price range offer improved resolutions, dynamic range and a host of other improvements, features & controls, making them suitable for the scanning of family photos and general small office applications.  Scanners in the $300 to $1,000 range offer improved quality and are targeted more to professional markets. Scanners selling above $1000 typically are devices usually offering larger scan areas and enhancements/features targeted to the graphics professional.

The standard scan area is typically 8.5 x 11 inches for scanning typical letter size documents (sometimes referred to as A4 size) or 8.5 x 14 inches for scanning legal size documents.  Larger format scanners coveted by engineers, designers and graphics professionals, typically scan 12 x 17 inches. Naturally, the larger the scan area, the greater the price tag.

Many scanners support the capability to scan in transparencies, negatives and slides. Some have a built in light table, while others require an adapter. Some will only handle 35 mm slides, while others will handle almost any photo format such as 35mm, 120 film, APS, 6x6, 6x7 & 4x5 formats. Other specialty scanners will accept 9x9 aerial formats as well as transparencies up to 8x10 inches and larger. The offerings run the gamut. A flatbed scanner with at least 1200 dpi minimum will suffice for the occasional non critical scan of a slide for printing a small snapshot, but MUCH better results are obtained by use of a dedicated film scanner especially designed for the task. Even the best flatbed scanner is no match for a half decent film scanner - it's not even a contest. Professional ccd based film scanners are now offering resolutions up to 5600 dpi, while high end drum scanners offer resolutions in excess of 12,000 dpi.

Old damaged photographic prints are often the only images to survive...  the original negatives having been long lost. Many of these early prints are in rough condition. If restoration of damaged photographic prints is your goal, then Kodak's "Digital ICE" technology warrants serious consideration.  The technology is a marriage between the scanner hardware and software.  Effectively, the scanner creates in addition to the R, G & B channels, an additional error mapping channel that maps the errors such as creases, tears, scratches & surface dust spots. The software based on the generated error map then applies corrections to remove the defects. It's quite effective on rips, tears, scratches and dust removal and can literally save hours of re-touching in Photoshop - especially on the "basket cases". Most corrections are virtually transparent with no softening of the image as is usually the case using software applications alone. Note however, it's effective only on reflective media and does not work with transparencies. Invoking the software (it is selectable) will easily quadruple scan times. However, considering that it may save literally hours in Photoshop, it's a small price to pay.  Currently, there is only one flatbed scanner that has "Digital ICE"...  It's the Microtek 6800 ($400 MSRP but they can be had for about $340 by shopping the net).  The scanner is  2400 dpi  (not the 4800 dpi they falsely advertise) and produces high quality scans with a Dynamic Range of 3.2. The next generation of high end flatbeds will undoubtedly adopt the Digital ICE technology, which is already being widely accepted and supported in many of the high end film scanners.  Note: Digital ICE is not a stand-alone software package, but works in conjunction with the scanner hardware especially designed for this implementation. It's not 100% effective..... you'll still probably have to do some Photoshop work, but this will greatly reduce the time required. If you have a large number of badly damaged photos to restore, this scanner for the moment, is the only way to go.  Quite amazing what it will correct !

Photographic prints typically yield no more than 300 resolvable dpi. The rule of thumb for the best results, is to scan at double the inherent resolution of the document to be scanned (ie: 600 dpi in this case) Scanning at higher resolutions will not yield any additional detail. All that will happen is an increased time to scan with much larger resulting file sizes.  If making enlargements from the original, then scan at a resolution appropriate to the degree of enlargement. ( ie: A 4x5 print scanned at 600 dpi would have to be scanned at 1200 dpi if the final print size was to be an 8x10). This is often better achieved by "adding pixels" through software such as Photoshop ® if you're already scanning at a higher resolution than that of the original document.

A better solution that will keep file sizes reasonable, as well as add the capability of image enhancement, is a software package by the name of Genuine Fractals.  It's not cheap, but the results more than offset the cost. If making large format prints from low resolution sources, then this software is an absolute necessity.

Note that most optical character recognition programs like to "see" scans at 300 to 400 dpi.

Even the best scanner gets dirty over time. Accumulated debris and dust accumulates on the mirror (s) and lens over time, reducing resolution as well as dynamic range. A simple cleaning can often return performance to new !

Over time, the fluorescent light source grows dimmer as the tube ages, making for muddy scans, poor color fidelity and poor dynamic range. Simply replacing the bulb will do wonders !

1. Beware that just because one model costs more than another, it's not always safe to assume that it will produce a higher quality print.  A higher priced printer usually offers larger print size choices, faster print speeds, networking capability etc etc etc, but none of these features affect the print quality.
2. Avoid the print resolution hype. Any printer capable of 600 dpi will be more than adequate. (At least until a 1 Giga Pixel camera comes along). Even 300 dpi printers (such as Dye Sublimation printers) are capable of true photographic quality. Color saturation, gamut , color stability & the availability of high quality inks are a much greater consideration.
3. As a general rule of thumb, the more inks, the better will be the color gamut (the range of colors capable of being reproduced).  A 6 color printer will make a better print than a 4 color printer. The print engine simply has more colors to choose from to "paint" the picture.
4. Avoid any 3 color printer like the plague if you're looking for photo quality. (Cyan, Magenta & Yellow only). A 3 color only printer will not be able to reproduce clean dense blacks and won't deal well with shadow details.
5. Some printers offer archival inks that are UV resistant and not susceptible fading. If the availability of archival inks is a consideration, this will narrow your choices considerably.
6. Media costs can quickly surpass any initial hardware costs. Though the printer may be a bargain, the supplies may send you to the poor farm. Less costly to keep fed are printers that have individual ink cartridges. Simply replace only the color cartridge that is depleted.  Multiple colors in one cartridge, require that you purchase a new cartridge when only a single color is depleted.
7. No manufacturer I'm aware of makes any reference to his printer making a lousy color print. The best way of judging print quality is to actually see the printer in action.