I would never recommend anyone purchase books in advance. Not only do you have to make sure you get the right one, but you might not even need the book to begin with. I've had three or four classes that called for a $250+ book, and I didn't open the damn thing once. Also, getting your books used, especially online, will save you a ton.
ETA: Come the end of the semester, I've found it's best to sell your books online, rather than back to the bookstore. You have to deal with shipping, but you generally don't get screwed.