Computer speed is not a big issue, 400 MHz seemed very usable, but 1.1 GHz is faster. Images are often several megabytes now, so system memory is extremely important. 32 MB used to be a lot, but it is quite inadequate today. People talking about 32 MB today probably mean in their video board. 128 MB is the norm today for Win98/ME, and that may be skimpy if you will print full-page images. You will want at least 256MB with Windows XP, and maybe more with a film scanner too. Memory is inexpensive now, think very seriously about adding more. Memory is too cheap to suffer now, just do it! Memory is the best single improvement you can make.
Disk space - YES! Lots of large images will consume lots of disk space, more than you can imagine. If you will be active, figure on several hundred megabytes space. Huge fast 7200 RPM 40 gigabyte disks are only about $120 now, and they make a very dramatic difference in speed.
In previous years when memory chips were expensive, video board memory was often too limited to allow large screen sizes. But today's boards have generous memory because it is cheap, and because 3D games need much more memory than photos. Video boards with 4 MB memory will allow 2D 24 bit color mode at higher resolutions (like up to 1168x768 pixels) on a 17 inch monitor, and 8 MB is fine for 2D on a 19 inch monitor, at say 1280x1024 pixels, or more. Scanner images are 24 bit color mode (needs True Color setting in Windows video).
Check at the Windows Control Panel - Display - Settings, to be certain 24 bit True Color mode is selected. If 32 bits is offered, select it instead, for more hardware efficiency than 24 bits (32 bit mode is faster, but it is still 24 bit color). If a larger pixel size or higher color depth setting is not available, it means there is insufficient video board memory present to support it.
If your video is set to 256 color mode for games, it will be very unsatisfactory for a scanner. If you are currently seeing poor quality photo images (but maybe graphics are OK), then your video system being set to only 256 colors is a common cause. Photo images will look bad at 256 colors. In 256 color mode, the 24 bit images from the scanner will be dotted and grainy, speckled and mottled. That is not the scanner image at all, it's probably fantastic. It's just that you can't see it due to the very limited way a 256 color video mode can show a 16.7 million color image. There is a sample of what this looks like on the Video board section page.
This is really an ambitious undertaking for me to attempt, there's just really no limit...
Scanning photographs for printing, for web pages, for Windows wallpaper, for emailing images to friends and relatives, images for newsletters or genealogical notebooks, for PowerPoint slides shown at meetings, etc, etc. And since these photos are now digitized, you can use editing software to combine images, create special effects, etc. This is an endless artistic field.
Flatbed scanners are very versatile for about all purposes except one. If wanting a huge image for printing 8x10 inches or A4 size prints on a photo quality printer, then a film scanner is much better. This is a limitation when enlarging the color print itself rather than the scanner, but scanning the original negative or slide is the answer.
Copying documents. Use the flatbed scanner with a laser or inkjet printer as a way to have a good copy machine at home. And unlike a real copy machine, you can use the scanner controls to edit and improve these documents too. A flatbed scanner is particularly versatile, and will allow scanning books and magazines without removing the pages. Some people mention that they scan their important papers and receipts as a way to store them (but frankly, that seems more awkward to me than putting the paper in a file cabinet). But I love having a copy machine at my desk now, it gets lots of use.
Faxing documents with a fax modem. You can fax text files from a word processor, but if that text is printed on a piece of paper instead, or maybe in a book or magazine, you can simply scan the paper and fax it too. You fax those scanned images the same way, by "printing" to the fax driver.
OCR - scan documents and use OCR (Optical Character Recognition) software to convert the image back to editable text, suitable for loading into a word processor. Most scanners include free sample OCR software, but for extensive use, you'd probably want to spend $80 for better.
What is OCR?
If you scan a page of text, like a magazine page, you will get a graphics image of the page, just like any other image. It is not text, it is a picture of a page of text, and can only be viewed or printed as an image. Its form is a graphics image, like a scanned photograph of your dog. Its form is not at all the same as if you had retyped the characters from the page into your word processor, which are individual text characters instead.
But the purpose of OCR software is to decode that scanned image of the page, decoding the individual pixel patterns, and it will generate real text characters in your word processor, the same as if you did retype the page yourself on your keyboard. This analysis of the pixel patterns is an easy job for the human brain, but it's a very difficult job for a computer.
Scan real items - coins, cloth, autumn leaves, the cat, whatever. Scanning fabric or wood boards can make some great textures, used maybe for your web page background, etc. 3D objects to be scanned should be more or less flat, without much visible height, well less than an inch for best sharpness. This is not to say you won't get good results with the doll or teddy bear, but the more distant parts will not be sharp or in focus. Shiny metal objects often cause reflection problems, and rotating the object, or perhaps tilting it slightly to change the angle, is about the only lighting control possible. The scanner certainly cannot replace a camera in every case, but it can do a lot. Lighting and depth are the main problems, where cameras offer much more control. But see more about the non-existant depth of field on CIS scanners.
Throw some things on the scanner bed and give it a go. These are real 3D objects, real flowers (Autumn flowers are intensely colored). Then the scanner bed was covered with a white sheet of paper, scanned at 150 dpi with the Black and White Points adjusted as described in the section A Simple Way. The colors are good, notice that the white paper is white, without a color cast. Then the spots were touched up with a Clone Tool, the image was resampled to half size for the web page and mildly sharpened with USM. Flat objects are better to scan, but life is a compromise. The paper on the right side is an inch above the glass, and the light intensity falls off.
Below are a few real sea shells, placed on the scanner bed and scanned at 150 dpi.
What did I forget? Things like scanning the kid's art to email to Grandma, all these things become very easy to do.
How did we ever get along without a scanner?
Hint: This scanned image was converted to a 16 color indexed palette using the "nearest color" method in Paint Shop Pro. It purifies the colors considerably (cleans up the muddy shades where one color gets mixed into the adjacent one), and it gives it more of a "poster" affect.