You could look into Emulation. If you own Forza you should be able to use the disk on your PC. Or create a backup of the disk and play from the ISO. This is not Illegal so long as you own the original. You will not be able to play online though. Check the steam marketplace, you might be able to find something similar.
OP, Need For Speed: Shift 2 (titled Shift 2 in most places) is the closest thing to Forza on PC. Dirt 2 and 3 and Need For Speed: Hot Pursuit might be up your alley as well. I'd recommend a wheel for Shift 2, Dirt 2 and Dirt 3. I'd recommend a dual analog controller for Hot Pursuit.