To all those people who bought Vista to play the vista-only DX10 titles, sucks to be you!
(And I almost was one of you, I have to admit)
Falling Leaf Studios, who make compatibility software, have decided they're going to make all those vista only games like shadowrun and halo2 run on XP. Their system will be released in the next few months, and will convert all the DX10 calls to openGL equivalents to run within XP. this may slow things down a bit, but it'll still be playable on a high spec machine.
A game cracker group, Razor1911, have beaten them to it and already released a cracked version of Shadowrun that does away with the DX10. The crack is only 5mb in size. I don't think its even technically illegal since you have to own the game first, this just allows u to play it on XP. Confusingly, the source I read specified that in the cracked version only "single player vs bots or multiplayer" is available. However, there is no single player campaign in shadowrun, its a multiplayer/bots only title AFAIK, much the same as the battlefield series (minus the new one)