In the game type in

iamacheater

this activates the cheat mode (you guessed that, eh?)

Now in the game you can press the following keys:

[C]   Add $10,000 every time you hit the key
[U]   Unlock all items
[S]   End Mission

Some more system tweaks (cheat mode not needed):

[Ctrl][I]    - Toggle Interface On/Off
[Ctrl][NUM+] - Increase Gamma
[Ctrl][NUM-] - Decrease Gamma
[Ctrl][[]    - Quit Game