Nice - that's very pong!
I have an idea for the ai.....when i hit the ball, have the ai make a random number.
Then on draw actor for the ai, have it say y=ball.y+random number.
Now you make the number like rand(80)-40;
Now sometimes the ai will hit the ball perfectly, but other times it will be off by 1-40 pixels in either direction (or whatever it takes to make it miss sometimes).
Also don't forget to post a screenshot!