Nope, there is no Gran Turismo game for the PC, what you've found are probably DVD rip's that somone has pulled off their PS2 disk's, either that or people are just miss-naming things because it gives them a buzz since they have nothing interesting to do in their lives. To emphasise the answer no there is no GT4 been made for any format other than the PS2. The only other format that has ever seen a GT game before is the PS1 and the PSP is due one soon, supposedly soon anyway.
Bear in mind downloading a disk rip is illegal though, and the site owner doesn't like you to promote such things on here.
