i've just read this tutorial http://www.rockpapershotgun.com/2010/01/20/rock-paper-shotgunity-post-12/ and try it, you can get the source code in this link
to move the paddle
Player 1: use Q and Z key
Player 2: user P and L key
to move the paddle
Player 1: use Q and Z key
Player 2: user P and L key