Make a file named "debugconf.scr" in the game "data" folder in the game directory with the following lines:

!include("DebugConf.def")

NoLogos()
Cheats()
UseDeveloperKeys()
LoadCheatMenuParamsOnLevelStart()

Press ESC during game play and select "Dev Menu" option. The following cheat options are now available.

AI Nicks
God Mode
Cheat Mode
Magic Ammo
Charge Full
Restore Health
Give Ammo
Give Rifle
Give Grenades
Kill Active Enemies

Enter 735S653J or 585A926D as a code to unlock extra money for equipment in Single Player mode, extra money for character unlocking in Multi-player mode, silver weapons in Multi-player mode, and the Superb Ranger weapon for use during the first two chapters.

Complete Single-Player mode to unlock the Very Hard difficulty setting.

Jumping and switching weapons while in mid-air is a great way to keep your current speed and momentum. This is useful if you find yourself being chased by someone in a multi-player game and are low or out of ammo for your current weapon.