I think using a microcontroller for something like this is too complex.
Your best bet is to learn to solder and follow this tutorial posted a few years ago. Its really not that hard if you are competent at soldering. You do have to use a DB-16 cable, not a VGA. Also, if you want to gain access to the analog thumbsticks, you need a DB-25 cable for the additional wires. This would only be for either a N64 or 5200 controller.
http://forums.xbox-scene.com/index.php?showtopic=510168http://www.xerxes3rd.net/staticpages/index...ontrollerOnXboxI followed that guide, along with the other directly below it (many thanks go to Scott over at Xerxes3rd) and so far I have successfully modded the following controllers.
- NES
- SNES
- SNES Advantage (w/o slow and turbo functions)
- SMS
- SMS Joystick
- TG-16
- Atari 2600
- Atari 7800
- Atari 5200*
- Genesis (3-Button)
- Genesis (6-Button)
* The Atari 5200 was a big pain to be honest, but with some patience, you can get it to work, even though it uses a flex matrix keypad. I'm going to be posting how I did that one soon, possibly this week.
Next up is a N64 controller. It will have to be 3rd party because Nintendo didn't use standard potentiometers in its thumbstick, so it would be impossible to use (I think). Luckily, the 3rd party controllers did use pots. I'm not entirely sure this will work, but I'm guessing the pots are standard 100k linear ones and if they are, they'll match up to the Xbox perfectly.
I'm going to eventually be working on an Intellivision, Colecovision and Odyssey 2 controllers as well.
I just got an Intellivision controller and it looks to be a big job, similar to the 5200, but entirely doable. However, I think I'm going to have to ditch the 16-direction control. If anyone knows much about this controller let me know. Its definitely an odd one. Like, what games even used that 16-direction movement?
Anyway, if you want to do just a NES or even SNES, its pretty easy and fun. My advice it to be patient take your time, practice and leave plenty of wire so nothing it too tight and causes a trace to be pulled up. (When I tried this for the first time, I dicked up this way. Live and learn.)

Also, I've found that glue guns (the cheap $5 kind) are very usefully for securing wires after your done. I usually hit it with an upside-down compressed air gun to freeze it instantly in place. However, keep that compressed air can away from the soldering and glue guns or kaboom!

By the way, I just looked at that Althack tutorial and its similar in concept, but man that is a ghetto looking rig! I mean, who wants to have a shoebox sitting next to an Xbox?
Good luck!
This post has been edited by DarthMingus: Jan 19 2009, 11:01 PM