Data acquisition of racing game signals

Hello guys,

I guess this will come across as a very odd question since what I'm doing may be a bit uncommon. Nevertheless, read along.

I'm doing a personal project in which I'm designing a gaming steering wheel - however I'm wanting to use alternative parts to save in costs. That goes with the need of processing input data coming from the game itself, which usually feeds these signals directly into the usb port where the controller is plugged in. For that reason, I must understand the signals to be sent to the controller I'm designing. Thus, lies the question: how can I capture these signals?

I've already found means of emulating USB joysticks, (http://vjoystick.sourceforge.net/) so I guess that's halfway there since vJoy is opensource. Also, I have a Xbox controller available for testing too. Does anybody know where to even start with this?

Thanks