Change the following line:

[Engine.Console]
ConsoleKey=0

to

[Engine.Console]
ConsoleKey=192

Save the file. IMPORTANT! Mark the file as READ ONLY (right click --> properties --> select read-only). This will keep the game from resetting the value to 0.

While playing, press ` (tilde) to activate the console, then type any of the following cheat codes:

Code:	Result:
god	God Mode
fly	Fly Mode
walk	Walk Mode
allweapons	All Weapons
ghost	No Clipping Mode
allammo	Tons of Ammo
invisible 1	Invisibility On
invisible 0	Invisibility Off
killall	Kill Everything
loaded	Get Everything

Unlock All Levels
Enter "2ndsquad" as your profile name to unlock all levels, movies, infinite ammo and supersquad.