Use a text editor to edit the "armyops.ini" file in the "system" folder
in the game directory. Add the following line under the "[Engine.GameEngine]"
heading to enable cheat mode. 

 bMPCheats=Enabled 2 

Then, press ~ or [Tab] during game play to display the console window. 
Enter one of the following codes.

Result                         Code 
-----------------------------------
Third person view            - behindview 1  
Unlimited ammunition         - mpcheat paramsammo 1  
No clipping mode             - mpcheat ghost  
Disable no clipping mode     - walk  
Weapon select                - mpcheat changeclass [weapon name]
Start game alone1            - start [level name]
Spawn indicated item or NPC1 - summon [item or character name]
Freeze game play             - playersonly