The best way to learn any toolkit is to build something using it. That's particularly true in the case of RoR, since it's very geared towards fast prototyping.

If you don't know Ruby, get the pickaxe book. I'd also recommend Agile Web Development with Rails:

http://www.amazon.com/Programming-Ruby-Pragmatic-Programmers... http://www.amazon.com/Agile-Web-Development-Rails-2nd/dp/097...

Also check out PeepCode; it gets rave reviews:

http://peepcode.com/