Here's a demo of a vulnerability I just discovered. The video description summarizes it.
http://www.youtube.com/watch?v=0P_3js9-H94&fmt=18
I was actually working on another app for this game when I found this. It was completely by accident. It's exploitable in all Halo versions and it's not patchable unless Bungie patches it themselves. I reversed a bit of Halo's engine, which is also ported to Halo 2...it's pretty much the same, plus a few changes/additions. I'm sure this would also work for Halo 2 vista without a doubt. I would release my src / research, but I have fear this will be another haloboom massacre! I will share this with Luigi though! Please just enjoy =]