you have only one problem with your request: you haven't noticed that there are major difference between real scanner system (the one in your link is pretty poor btw) and n900's image module.

with real scanner system you have a large format lens fixed and scanner drive head moves at the image plane of the lens just like it would move in scanning plate.

first thing you would need to do is to get a fixture that allows rotation along optical axis of n900. without it the whole stuff is completely useless.

or is there some weird point for it outside getting more resolution out from n900's camera?