Discussion of scanning just for the practical matter of posting images in the galleries is permitted, so as long as the topic stays there (I've updated the thread title to promote that) and doesn't get into the more involved questions of what scanner to buy or digital printing, the thread is okay. If there are good answers, maybe we can make it a sticky to discourage the proliferation of such threads.
Generally for the APUG galleries images should be in JPEG format (GIF is also accepted), no larger than 850x750 pixels, in sRGB colorspace, and no larger than 512 Kb. Sometimes images that are within the maximum size in pixels will be too large in Kb, so you may need to use more compression (lower quality) or post a smaller image. I tend to post images that are 650 pixels on the long dimension, unless they are panoramic formats, and then I'll go 850 pixels.
If you are scanning prints, I'd recommend scanning at 300 dpi, and then adjusting the curve or levels so that the image on your screen looks like the print in your hand, spotting if necessary (since scanning or duping is another place for dust to get in), downsizing to the size you plan to post at in the gallery, and then sharpening the image slightly to compensate for JPEG compression and the effects of scanning and resizing. I usually work on the image in TIF format and save as JPG as the last step after sharpening, because JPEG compression is lossy, so each time a JPEG is saved data is lost.
Some paper surfaces don't scan well, and prints need to be as flat as possible for good results with a flatbed scanner. If you are getting a lot of surface artifacts with the flatbed, you may be better with your digital camera on a copy stand or a tripod with a lateral arm using standard copy techniques (search for the many threads on copying flat art), and possibly cross polarization if the print isn't flat enough to avoid reflections or if the paper surface is very textured.