You can't. Even if you got a "patched" version or whatever they call it that claim it's DirectX 10 on Windows XP, it's not real and will never be on Windows XP.
If you want DirectX 10, you need to get at least Windows Vista.
Take a seat everybody, uncle t4ct1c47 is going to give you a brief history of why misinformed people think that DX10 will work on XP.
When Vista was first released, Microsoft tried to take advantage of every possible selling point. When they released Halo 2 they made it so that the game would only work with Vista. Halo 2 never needed DX10, Microsoft simply wanted another reason to persuade people to upgrade from XP.
When you first install most programs the installation process will perform a few basic checks to make sure that your system is of sufficient spec. For example, when you try to install Crytek's Far Cry onto an old Windows 95 machine you will get an error message saying that the operting system isn't supported. In the case of Far Cry, this was true, as the game needed DX8 to run and Windows 95 doesn't support DX8.
In the case of Halo 2, a game that was originally released on Microsoft's X-Box which didn't use DX10, there is a similar check to make sure that the operating system is Vista. However, as you've no doubt guessed if the original console game didn't use DX10, then the PC version won't need it either. The only reason Halo 2 doesn't work on XP is because of one of the checks performed when you attempt to install the game. There is crack available, that bypasses this system check, and allows you to play Halo 2 on XP.
Pretty much since that crack came out people started to think; "If one game that requires DX10 can work on XP so can others". But that's the point, Halo 2 never required DX10. Now when it comes to people who claim that they were able to install the D3D10 API onto Windows XP, there is a big difference between physically copying the files to the machine's HDD and actually getting the operating system to run them. Although there is a way to make it so Windows XP's DXDIAG reports the DirectX version as DX10, it doesn't mean that the machine is actually running DX10.
The Direct3D API was specifically designed to run on Vista. Attempting to migrate an entire API from one system to another is no mean feat, if this was the case, Linux would not still be relying on OpenGL. I hope that is a clear enough explanation for you.
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