Here is the way to download halo dev trainer and use the awesome cheats!
1. Look up Halo dev trainer on google and select the first thing.
2. You should be on halo maps.org, go down on the page a little bit then press the red download button.
3. Look for something called dev trainer in your documents or applications page.(It's icon looks like a purple masterchief.)
4. Copy and paste the dev trainer on your Halo game and create a shortcut for your dev trainer.
Then just play your game! Oh, and don't pull up your dev trainer until after you start the level. To activate the cheats, just minimize Halo and click on the cheat that you want. It should light up green.
P.S. They don't work to good on multiplayer.
Added by: Talon9889 Jun 11th 2009, ID#14025