The BVG rules:
1.) Do not impersonate others (with your posts or profile).
2.) Do not advocate cheating or grieving behavior.
4.) Do not discuss unauthorized modification of console game hardware or software, even if you're not trying to cheat or pirate.
5.) Political or religious discussion is prohibited, even in the Off Topic forum.
6.) When creating new threads, be sure to post in the correct forum.
7.) Do not use the public forums to run contests, solicit donations, barter or sell items/services, or advertise anything at all.
8.) Respect your fellow members, or at least tolerate them publicly. Harassment of any kind will not be tolerated, even if they probably deserve it.
9.) Use common sense. This is a video game developer's website. Keep your posts on topic and "safe for work." The further you stray the more you tempt a ban.
10.) Do not post about any illegal substances or activities.
11.) Do not spam any any way, shape, or form. This includes the forums and private messages.
12.) Just don't Be stupid. It'll save both you, and us a lot of trouble.
Now, #4 is probably why you couldn't post your Halo 2 thing Jony. Some mods are authorized though. Practically everything in Halo 1 is, but I'm not sure about Halo 2. I know making custom multiplayer maps is fine, but Halo 2 has achievements, and they probably don't want you messing around with their campaign.
Where is rule #3???