Depends on your school and how their tests are. At a minimum, I would not recommend spending money on anything before asking upperclassmen at your school if the textbooks are (a) necessary and (b) available somewhere for free. At my school, you basically don't need to buy books except whatever you want for board review.
Yep, find an upperclassman and ask. We got tested on powerpoint and on reading. We all basically bought the books, and they were helpful but expensive. The library had multiple books, but they were always checked out. It's a game: where do the professors hide the answers to their questions?
It also depends on how you learn, and your approach. If you like books and learn well by them, buy 'em. If books are not your thing, but profs test out of them, read them in the library before the test. I think most schools are going to power-point-heavy-content-rich approaches with textbook recommendations (i.e. read in the library ahead of time.)