We will have to disappoint all of you with a little hope left that DirectX 10 will find its way to Windows XP. At one point we believe that this will be the case but Microsoft was officially very clear on the matter.
The MSDN people were the first to hear the bad news. When asked, Will DirectX 10 be available for Windows XP? Microsoft officially replied.
"No. Windows Vista, which has DirectX 10, includes an updated DirectX runtime based on the runtime in Windows XP SP2 (DirectX 9.0c) with changes to work with the new Windows Display Driver Model (WDDM) and the new audio driver stack, and with other updates in the operating system. In addition to Direct3D 9, Windows Vista supports two new interfaces when the correct video hardware and drivers are present: Direct3D9Ex and Direct3D10."
So the hope is lost and the official statement is here, just concentrate on the first two letters of the statement.