How to learn BEAM robotics?
I really liked "JunkBots, Bugbots, and Bots on Wheels: Building Simple Robots With BEAM Technology". It does a really good job of introducing the BEAM aesthetics, such as they are.

However, if you really need to start from the beginning, Robot Building for Beginners (Technology in Action) might be the best place to start. It's very thorough, and gives what is probably the best advice I've ever read: "Stop being a visionary and start building something." There's no substitute for experimentation!