Open up your hitman.ini file located in your Hitman directory. Add the line 'EnableCheats 1' to the file. When playing a mission, hit the '~' key. Types any of these codes:
SPECIAL NOTE: Some have noted that you can simply type the codes in while playing (with CAPS LOCK on) instead of using the console. You can also try adding the line 'EnableConsole 1' to the hitman.ini file to enable the use of the console.
|IOIGIVES||All Weapons with Max Ammo|
|IOILEPOW||Lethal Charge Mode|
Access All Missions
Open up your hitman2.ini file and change:
Start the game and you will get a level select menu, with all missions unlocked.