I believe, that as long as you don't sell a copyrighted product, say a Master Chief character or a Bloodgulch map, you shouldn't be in any trouble unless your selling a product with a copyrighted object in it.
Like, Red vs Blue, that was a comedy based off Halo 1, 2 and 3. It was a none profit project, that eventually became a top seller once Bungie and Microsoft allowed them to sell it under them.
Like, the Half-Life 2 Zombie on these forums was none profit, and alright as long as nobody used it in a commercial game.
So, I believe your alright, if Microsoft or Bungie bugs you about it, tell them that It was a none profit project and legally you've done nothing wrong.
I believe you're alright, check out this site:
www.theforce.net
It's a site stuffed FULL of Star Wars Fanfilms, as long as it's a none profit project, you are perfectly alright.
Edit: Check out this: http://www.fpscreator.com/pack11.html
Scroll down to MP 12 and you might see that it includes 6 Halo Spartans in it. The only difference in why they were allowed to sell it was they added a big backpack to it. So, you're completely safe.
