I've honestly never heard of textbook rentals (aside from those in libraries here and there), but I usually just buy textbooks at half.com. Haven't had a problem with any of my purchases so far, and I almost always sell them back that way as well, like Link927 does. Usually college classes have the names of the textbooks online, so you can have them on the first day or week.
I dunno about you guys, but putting aside the time it takes to scan/copy pages from a textbook is a little extreme, even for a cheapass like me. 'Course, you would probably be saving a lot of money by doing so, but in that time, you could probably make money by working or something