PHP books/tips to get started?

Hello everyone,
I haven’t installed or done anything with WordPress yet, because I don’t know anything about PHP (and it sounds like some PHP knowledge is required, or at least very useful). I don’t want to wipe out my existing CMS without knowing my way around a new one, ya know?
So I’d like to know if you guys could recommend any PHP books for beginners, or any PHP tutorials online for beginners.
Also, I’ve heard of people running their WordPress on their computer and fiddling around with it first, before installing it on their server. I’d like to know how this is possible, and how would I replicate this on an OS X machine (I have a Powerbook 12″).
Thanks,
Nicole