Easiest would be to find an adapter and use that.

If one doesn't exist, you'll just have to make your own.
If your wheel uses either 100k ohm or 5k ohm pots, then you could interface it via something like Dave's AKI joystick to USB interface.
http://dave.bit2000.com/Assuming you want to keep using it with your PlayStation, you'd need to find a compatable socket for the wheel's plug, and then wire it to the interface. If not, cut the plug off, and wire it directly.