This shows how to get your Xbox wireless controller up and running in RetroPie and the RetroArch emulator on the Raspberry Pi.
Here is the wireless receiver I used, about £4 on eBay:
http://images.doba.com/products/3400/...
I used an official Xbox 360 wireless controller:
http://img4.wikia.nocookie.net/__cb20...
The "pair/sync" button is here:
http://compass.xboxlive.com/assets/bd...
Install instructions I followed:
https://github.com/petrockblog/RetroP...
This thread is also useful:
http://blog.petrockblock.com/forums/t...