Hi there. Just thought I would pitch in at this stage. I think we have all arrived at the correct conclusion now. Scanners further complicate the issue, so here are my tips for this. For a start, forget you ever heard the term "interpolated resolution" Gee really - of up to 1800 dpi? Find out what the OPTICAL res of your scanner is (usually 300 or 600) and scan image at that res. Then resample to the actual size (in pixels)you want in Photoshop or whatever, and slap unsharp mask on it. If this makes for really unweildy file sizes, then go with 50% increments. IE if you have a 600 ppi scanner, then scan at 300 or 150. All you really want from a scanner is an image as nice and sharp as possible. You can't expect the built in software on a £100 scanner to achieve any acceptable results. The resampling engines on Photoshop and PSP are actually built for the job, so use them instead.
I'm glad this topic came up and some Xarans have been enlightened. I know i was really confused about the whole issue for ages. And yeah..those respected expensive big books don't explain it either. 72 ppi indeed! Pah! For further reading on scanners and resolution, I would highly recommend http://www.scantips.com