You must be running the Alky project or KM stuff then. Microsoft's official position is that XP only goes up to 9c. The items above are unofficial ports of DX10 to XP. Nothing wrong with that - in fact I applaud those groups for doing it! Just know that its not "official" so if something screws up, MegaShaft - uhm - Microsoft isnt going to support anything. Like they would anyway?
When cash allows - move to windows 7.
Games that use DX10 can still run on XP only using DX9 - DX10 games are all "backward compatible" in those cases - if 9 is there they run fine - if 10 is there you get the extra bells and whistles that 10 brings to the table.