After a few minutes trying different strategies:

If I win the coin toss I'm winning the game, every time. If I lose the coin toss it always ends in a draw.

Transcript (of 7 wins): http://dl.dropbox.com/u/142733/tictactoe.txt

Assuming I win the coin toss, I always choose a corner for my first move. The CPU should then take the center but it never does. This ensures I always win.

That said, great job so far. It's very close to perfect IMO.