I'm going to be a Junior this following year, should I study for SAT or PSAT?

So I'm going to be a Junior this following school year and I should really be studying for some important tests. But which one? Last year (as a sopre) I took the PSAT just to try it out. I did okay and I'm definately retaking it for real. But I'm also aware I need to take the SAT somewhere in the year.. and also with collegeboard.com/quickstart (its for anyone who took the PSAT) it gives some review and lots of practice, it seems, for the PSAT. So if I wanted, I could just study the PSAT off of there. The problem IS I want to buy a study book to study on and I'm not sure if I should buy a SAT book or PSAT book.. help?!