Hi, I looked up the XInput documentation a while ago, and the DLL seemed rather small and simple to me. My quick uneducated guess is that it should be pretty streightforward to wrap it to the standard joystick API.
What I recommend you as a start is to boot Windows, get some Windows development tools and experiment with the XInput API to understand how it works and get some test cases. This may require you to buy an Xbox 360 gamepad, since XInput only talks to this hardware. Once you understand how to use xinput.dll, you'll have a much easier task implementing it for Wine.
