A Few Scanning Tips" it is a whole lot more than that.
There is so much fascinating information on this site I hardly knew where to start. So I chose the 72 dpi debate as this is the one that seems to crop up most frequently. The article you need to read is called "Say No to 72 dpi". Wayne not only talks a good talk he provides visual proof of his arguments as well.
Did you know why you should download images off the internet rather than cut and paste them? I suggest that you have a good look around Waynes site, it is a goldmine of fascinating information.
Other useful websites I came across whist looking for this information are included below.
Scanning and Printing Resolution Calculator
Image size Calculator
Fotosizer - Batch image resizing