
DX9 and DX10 don't conflict they are different and your on XP so forget about DX10. DX is an opperating system component. DX9 with WinXP DX10 with Vista.
DX10 will run DX10 or earlier, so if someone has Vista, all of there old DX stuff still works, if you have a game in Vista that is DX10 enabled, it will be able to make use of those enhancements in DX10. If not, it runs in DX9 mode, no conflicts.
Forget DX10... you can't download it or install it, the only way you can get it is if you change to Vista, its part of the OS.
Yes in will run in XP... just download the drivers from http://www.nvidia.com.