it is relatively well known that XBox controller ports are essentially USB ports, so the connection is simply wire to wire. I'll include a diagram below, but the big thing to remember is: skip the pin that had the yellow wire, and don't short it (the yellow wire apparently carries 12 volts.
first, bend all four pins on the USB Connector to face outward from the back of the connector. looking down from the top, bend the left most pin slightly to the left, and the other three pins slightly to the right, to make room for the unused pin.
solder the connectors together, following the diagram
now here's the secret I didn't learn until late in the process. Short the ground pin to the metal shield of the XBox connector (this corrects lots of connection issues). test your connections before you go any further.
USB PINOUT KEY
4. -5v (Ground)
XBOX PINOUT KEY
1. -5v (Ground)
2. +12v (Unused)