I made a tutorial, found
here, that shows a good Xbox to USB converstion.
It allows you to use your Xbox controller on your PC while still being able to use the controller on your Xbox as well. It doesn't look like shit either.
The finished product looks just like a normal Xbox cable, but with a USB connector going out of the top (where the circular indentation is).
I'm pretty sure this would also work as a USB adaptor for the Xbox. All you would have to do was add a female USB end in place of the male USB end. Also, for it to work that way, you couldn't have the controller plugged in at the same time as a keyboard or mouse.
Also, is there any driver available that allows full functionality of the Xbox controller on the PC? I'm currently using the Xctrl driver (link found in tutorial), but this doesn't allow use of the L and R triggers, as well as the L and R joystick buttons (pushing down on them). Is there a driver that allows the use of those buttons? Other than that, the driver works great.
http://xbox20-02.tripod.com/ledtutorial/id9.html