Note: This editing step is only required in early versions of the game. Versions 2.3
and later should already have cheat mode ready to be used in single player mode. Also
note that editing the file will not allow you to use cheats on player operated servers;
only the operators can activate them, at which point they will be activated for all 
players who join that server. No file editing is necessary. For all other versions, 
this procedure involves editing a game file; create a backup copy of the file before 
proceeding. 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 to activate the cheat function. Note: Some codes such as 
summon and avatar have been disabled in later versions of the game. 
 
Result                                  Code
--------------------------------------------------
Invincibility                         - mpcheat god
Toggle third person view              - behindview [0 or 1]
Toggle unlimited ammunition           - mpcheat paramsammo [0 or 1]
No clipping mode                      - mpcheat ghost
Disable no clipping mode              - mpcheat walk
Medic capabilities                    - mpcheat medic
Spawn various binoculars              - mpcheat binoc [1-5]
Spawn night vision goggles            - mpcheat nvg
Spawn indicated weapon2               - mpcheat changeclass [weapon name]
Supress mpcheat changeclass message2  - mpcheat silentclass
Start game alone1                     - start or open [level name]
Spawn indicated item or NPC3          - summon [item or character name]
Set game speed                        - mpcheat slomo [-1 to 9]
Control spawned NPC3                  - avatar [character name]
Make some spawned NPCs walk           - walk
Remove all characters                 - killpawns
Record multi-player mode demo         - demorec [filename]
Stop recording demo                   - stopdemo

1. Requires the v1.9 patch.
2. Your newly chosen class will be announced to all players on the server unless 
   the mpcheat silentclass code is used.
3. Only available in certain older versions of the game.