There is no game that particularly work on XP and not on Win 7.
I'm not so sure that's completely accurate. From the games I listed:
Rally trophy does not function properly under Windows 7; I know that for a fact because I just tried it to play it within the last month.
I've never been able to get Crimson Skies to work under Windows 7, but the last attempt I made was a while ago.
DTR and DTR2 wouldn't even install in Windows 7. As a mater of fact - a lot of my old games from that time period wouldn't install correctly in Windows 7.
Why do you think I would go out of my way to buy an XP machine if everything played great in Windows 7?