I'd say to buy FileMaker Pro and see what you can figure out. It is really easy to use. Then if you can't figure things out, can't find help online for free, or want to do very advanced things go to the bookstore and see what they have that will meet your needs.
My copy of FMP6 came w/ the User Guide and Quick Start guide, which I haven't even opened. Been using it since version 4. You should have no problem getting started w/ those 2 books. Buy a bible only if want to get into advanced stuff.