Get your xbox controler end and bare the wires near the easy out end,now cut into the usb keyboard cable and bare the wires. Now match the colors red-red black-black green-green white-white yellow-nothing (cut it) there might be a second black wire in the usb side...you won't need it. Now solder it up and seal it with some heat shrink and you should be good.
or you can use one of these http://www.xbox-modchips.com/xenium-led.htm to get a light and a easy usb connection