This is an old rumor....nothing more. So far we haven't seen any proof of this game. I think that once this was a serious project but the gamezilla Sony use its influences to asure the PS2 only on this title. Also given the low sales of racing games on the PC it didn't had the incentive.

www.computerandvideogames.com/stories/pc/ gt_professional_pc_rumour_skids_off_track.html