Long story short, the ex-Vice Prez of Microsoft's gaming division has created a Atari 2600 Halo game that you can play right now online.
Here is the article link at IGN http://xbox360.ign.com/articles/110/1109805p1.html
or
If you want to get started playing right away here is the link to the game http://www.codemystics.com/halo2600/
