Is it possible to rig an xbox game so that you can play it on your computer.

I want to use my thrustmaster steering wheel with Forza 4, but the xbox doesn't support it. Is there any way to play forza 4 on my computer or use the thrustmaster with the xbox?

The Xbox 360 (and original Xbox) are basically modified PCs. Emulators for them (if successful) have only been able to play one or two games in the past.
For emulation to be possible, the computer needs to be four times more powerful than the system it's emulating. So with today's computers, you'd still need to wait a few years yet.
As for making the wheel work with the Xbox 360....it sounds far-fetched to me, but I'd say see what you can find online.
The xbox 360 is comprised of a 3.2 GHz 3-core CPU, 500 MHZ GPU, and 512 MB of 700MHz RAM shared between the GPU and CPU.

It would be hard not to build, or buy, a computer more powerful than either xbox and reaching this alleged 4X number is not a stretch (Remember it's not just a matter of multiplying the numbers). In fact the XBox One, and the PS4 for that matter, would only be considered Mid-range gaming PC's.

The issue with emulation is more of a software and architecture problem. The hardware for the xbox has been customized so it isn't quite the same as PC hardware meaning running the custom xbox firmware on the PC is problematic, regardless of having a very powerful computer.

Blacksmith98: You're much more likely to find a work around for the wheel than the xbox.
You won't be able to play the game on the PC. Xbox goes through great lengths to make the games only playable on the console. I doubt you can find a workaround for the wheel to work on the system. BUy look around and see what you can find. Maybe someone was able to make a hack or special driver for it.