you don't need directx 11, I used it with directx9 and it worked just fine.
one thing that made it work for me was first of all, use a different injector other than the mpgh one, secondly run the injector as administrator and also run the game as administrator.
i don't think windows xp can run directx 11, i think there is a hack for it to run directx 10 though, but i wouldn't fuck with that unless you are absolutely sure your graphics card can use directx 10 and also that you know your way around windows enough to revert back to directx 9 if it didn't work.