At the main menu press Shift+Keypad Minus and type 'campaign'.
Bonus level
Successfully complete the game with the best ending. Allow the credits to complete and an intermission sequence will begin.
Cheats for demo version
Start your mission and go until you get to the helicopter. Wait a few seconds and jump out of the helicopter. Jump out before they start screaming about the helicopter getting hit. You will become invincible until you go to the Target area and finish the level.
End current mission
During gameplay, pause and press Shift+Keypad Minus and type 'endmission'.
Evac level
Use the following tactic in the Evac level where you have to drive a truck. Go to this grid code to join the Guerillas Fia EA64. On the map there will be a code 113. Drive your truck there. An intermission sequence will appear, then the level will end. You will be a hostage for the Soviets. Stay in the tent on the next level until the Russian that is guarding you dies. Then, go outside and one of the guerrillas will talk to you.
God mode
At any menu, hold down left Shift and type -iwillbetheone.
Unlimited ammunition
Simply reload before you run out of shots on one clip.