Xbox:
733MHz Pentium3 with only 128k cache
233MHz nVidia chip(basically work in progress between GF3 and 4)
And no, you can't just send the CPU instructions to your CPU. You would need a full emulator. Also, the games don't send D3D commands, then are compiled using D3D, but the game itself sends the data as a direct register command to the GPU, and no one I know of has the full register level specs for Geforce3/4 hardware
This was talked about by a few MAME devs, and trying to emulate Xbox on a 733MHz normal computer was a joke.