Okay so i was looking through the code to the avatar editor flash thing on the xbox website when I came across another site which I explored a bit and found the halo 3 toolkit. Posting a direct link is probally against xbox terms so ill just post a link to google and say use the top 2 links, they both work. BTW the second link is the site I found it on. Looking around the official halo 3 xbox page there doesnt seem to be a link to this so I could say i've found this halo 3 toolkit - Google Search EDIT: There is actually a link to this page on the downloads page for the halo page so sorry about that But for those who dont know about this enjoy.
I found this yesterday, just so you know. Anyone that was in the Tester's Guild IRC can vouch for me on that. And it's not against the Xbox ToS to post a link to their site... LOL.
The rest of the world found it before Halo 3's launch! That 'toolkt' is old news, notice how only the Beta maps a Bungie's render's are used? Its nothing new.