How do I read a playstation 2 controller's output with a teensy?

I have an idea for a project that would take a playstation 2 controller and view its output. The protocols REALLY confuse me. Can someone find / make me code to see the button presses? More specifically, I have a DDR mat that I'm using, but it works as a controller for the game, so I figure the concept would be the same. Any help is greatly appreciated. If you need more details, I can be reached at DFTBA(four)ever at (Replace the four with a 4.)

You're awesome!