I have sent Dibya a PM with the update package.
It will take much more work to be a full backport.
For example, the dxgkrnl.sys, updated dxdiag, patched rpcrt4.dll, version.dll, cdd.dll, ntoskrnl/HAL files
It requires advanced knowledge of the kernel structure. Recommend analysing the manifest files in Windows6.0-KB971512-x86 to get a first idea of the files needed. Then try understanding how this update brings DX11 functionality to Vista and try to combine this with DX10 in XP kernel.
Remember: there is no way you can avoid changes in kernel, due to dxgkrnl.sys