There is no such thing as full DirectX 10 on Windows XP.
And besides, Dx10 gains no benefit over Dx9 as Dolphin only makes use of Dx9, even if you have Dx10, you will need to install Dx9 seperately in order to use Dolphin. That's on Vista/Win Srv 2008, as I said; there is no such thing as Dx10 on XP.
__________________
Vista Home Premium
Intel Core 2 Duo 1.66GHZ (T5450)
2048MB RAM
Integrated GFX: Intel X3100 358MB (Chipset: Intel Mobile Express GM965 (Pixel Shader 4, DX10))
(Toshiba A200-1YO Notebook)