What you will need:
Xbox controller, preferably the S type, although either will work.
USB cable with at least 6 inches of actual cable on it.
electrical tape, although duct tape will probably work.
soldering iron and electronics grade solder(OPTIONAL)
WHAT THIS WILL DO:
Threw the use of 3rd party drivers( which you will need to download HERE
after you are done ) you can use your Xbox controller as a joystick/gamepad for your computer as well as have access to the MEMORY CARD for storage/soft modding. Works great as a gamepad for emulators/roms.
DO NOT BE INTIMIDATED. THIS IS VERY SIMPLE.
Inside your Xbox controller cable, there are five wires; Black, Red, Yellow, Green, and White. Inside a USB cable, there are four wires; Black, Red, Green, Yellow. The black and red wires for both cables supply 5 volts. The green and white wires are used for data transfer, also supplying .3 volts. The Yellow wire in the xbox controller is used for the Light Gun controller, and isn't going to be important.
If you have the S controller, detach the break away cable that attaches to the xbox.
1. If you have the S controller detachable cable, take the small detachable cable and cut it in half.
If you have the old controller, cut it off about 6 inches away from the end of the cable.
2. Cut away the plastic on both sides of the cable you just cut about an inch and a half so that there is an inch and a half of exposed insides of the cable. If there is a foil sheilding around the wires, cut it off at the inch and a half mark, and if there is a un-covered set of silver wires you can cut those out to.
3. Strip off a half inch of plastic coating on each wire on all sides.
4. Get your usb cable, cut off atleast 6 inches of the cable( make sure you have the male connector on the end ) and repeat step 2 and step 3 for the other side of your usb cable.
5. You should now have stripped 14 colored wires in all. Now all you need to do is match them up and wrap them in tape, or solder them and wrap them in tape if you desire.
6. When you hook it to your computer, make sure you have your drivers installed and there should be a XBCD setup program installed on your computer that will let you test to make sure it worked.
I have done this to three xbox controllers and never had a problem with any of them. Great fun playing roms with a bunch of mates on your comp with xbox controllers.