Ok I found the story on Halo2 PC. Its actually a mod using the Halo editing Kit. Since this software is availible for Halo PC users only, essentially what these people are doing is creating Halo2 from Halo. They made New Mombossa a multiplayer level, and did some other kool shit. Check out the link if you wanna read the whole article.Halo 2 PC article.