the nv sdk contains nvut, which contains support for using .x files in D3D10.
it works, I have used it.
its slightly ugly, though, in that it creates both devices, locks the D3D9 vertex and index buffers, and copies them into D3D10 equivalents.
http://www.futuregpu.net ex-Aces Lead PM/ex DX SDK PM/ex D3D Evangelist now LRB Launch Native Title Wrangler