William Petersen might want to investigate the terms of his CSI deal. As reported here yesterday, the actor hinted in the current issue of Playboy magazine that he might leave his gig on TV's No. 1 show "at the end of next year." But before you could say "negotiations ploy," a CBS source presented TV Guide Online with some rather damning evidence: Petersen is contractually bound to play Gil Grissom through the 2006-07 season.