Cheats:

 Everything starts with [P] [Backspace]

 arjan   - HAHAHA displayed on screen
 gunhed  - gives you all weapons
 tim     - displayes AWESOME on screen
 check   - displays some numbers on the screen
 greetz  - opens an "Arjan Greetz" window
 doom    - flashes the screen red (ar-ar!)
           plus there's another little thing I won't tell you about..
 lamer   - jump to next level
 mark    - will lose a life and start over
 apogee  - toggles between 16-color EGA and normal
 bouf    - temporary invincibility
 sable   - super sonic speed
 cstrike - gives you the air-board
 hooker  - takes you to bonus level when current stage is done
 bad     - gives you the bird *yuk-yuk*
 ken     - don't know what it does
 hocus   - teleports, provided you have an enemy above or below you