For Conscars, +rep for that post. I know from experience releasing content for a racing game (and that's small-time in comparison to mapping for Halo) that making "tutorial" maps or vehicles for a game leads to all sorts of people angry that their time's been wasted. For the racing game I simply moved a dozen vertices or so on a 50-poly vehicle model, re-skinned it and released it as my own. BIG MISTAKE! I still have the scars...

Please people, don't repeat my mistakes. Practise, go through tutorials, maybe ask the experienced mappers a question or two (though in one thread, not fifty), and make sure what you're releasing is on par with what the community expects. PLEASE!