It is actually really easy! Just download an application called JoyToKey. Then, you simply remap the buttons on the joystick/gamepad. I did this with an old PS1 controller I modified to use on the parallel port.
Now I want to ask a question:
I used a bluetooth adapter and was able to communicate with my Wiimote and Nunchuk controllers. Thus, over BT, I incorporated in GlovePIE, a free scripting software. Basically, I used an IR sensor as well, which I also built. Thus, using GlovePIE, I ran a script which converts the wiimote into a mouse, and uses the nunchuk for WASD movement. Now this was an FPS script, designed solely for FPSs. However, if I run it, I can use the wiimote as my mouse, but in CA or any FPS game, it doesn't work at all. I dont get errors, but my mouse doesnt move. The cursor doesnt move at all, and I can't play the game.

Anybody got any ideas?
(YAY!!! One of my first posts!

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(Climb aboard Choobs! Let's ride the Choob-Choob Chrain ^^)