To unlock all of the levels in the game, you will need to edit a game file; creating a backup before proceeding is recommended.
1. Create a new profile 2. From Windows, locate the 'checkpoints' directory for the newly created profile. This should be located in D:\Documents and Settings\...\My Documents\My Games\Halo\savegames\All_Levels\checkpoints 3. In this directory create a text file called checkpoint0.sav with the following text included: 0,0,0 0,0,0 0,0,0 4. Repeat the previous step until you have ten files named checkpoint0.sav ... checkpoint9.sav and for each file change the first number on the first line to indicate the level (such as 0 The Pillar of Autumn)
1 - Halo 2 - The Truth and Reconciliation 3 - The Silent Cartographer 4 - Assault on the Control Room 5 - 343 Guilty Spark 6 - The Library 7 - Two Betrayals 8 - Keyes 9 - The Maw
For example, for 'The Maw' level, you will have add the following lines to checkpoint9.sav:
9,0,0 0,0,0 0,0,0
Play Campaign and Load Game. You should now have access to all the main game levels.