I'm preety sure Windows XP SP3 will have DX10. But for it, there are little, if not any, games that are available. Now, the DX10 games are a big improvement, but you'll need vista and a DX10 compliant card. Not a lot of us has that. It's all in the matter of time.
In a year or two, Windows XP will be like Windows 95/98/ME and eventually, 2000; outdated and support ended.