There is people that is trying to port the dx10 features to xp and as far as i know there is a variant in the alpha stage.
But how it works and if it works, i dont know.
And beside all that you need a game/appliction that is made for dx10 and there is not many of them.
Ive been running Vista since it came out and i think i have just 2 games out of many that is for DX10.
And you need a real good computer if you are gona take advantage of the dx10 feature. More or less the latest is necessary to get the full advantage of dx10.
Iam one of the few that really like Vista
and i wud never go back to XP.