I bought a Microsoft XBox 360 controller with the intention of having a console quality gamepad on my PC and Mac. Thus, knowing that it only come with Microsoft drivers, which only supported rumble using the Xinput API which no games seem to support yet, I also had the intention of finding out how it works to create my own DirectInput/MacOS X drivers.
Just before Christmas 2005 I spent about a week looking into the USB reports sent and received by the controller, so as to understand the readings from the buttons and axis, how to control the LED and the rumble motors.
The information found can be viewed on this page.
After I discovered the means to control the LED and rumble motors the people at Free60.org updated their gamepad page with my findings, which was then inserted into an updated driver for the original XBox controller.
Matt's altered XBCD driver for Windows can be found at http://www.matt-land.com/xbcd
After making these findings I implemented a driver for MacOS X. It can be found here.
(Please note this page was originally found at http://mice-software.com/other/xbox.html)
Then, in January 2007, it turned out the Microsoft Wireless Gaming Receiver for Windows was out. I went down to a local electronics store to pick one up, specifically with the intention of making it work on MacOS X. After some investigation it seemed fairly straight forward, and so implementation of the driver proceeded.
If you're looking to buy a 360 controller or other related merchandise, you can support my driver using my affiliate link:
Amazon.com: XBox 360 wired controller XBox 360 Store
XBox 360 Gamer Card
In case anyone's interested, I finally got an actual XBox 360.