Before each code, press "p" and then the Backspace key. 

gunhed-gives all weapons including bombs 
arjan - HAHAHA displayed 
tim - AWESOME displayed 
check - displays numbers on the screen 
greetz - opens an arjan greetz window 
lamer - jump to next level 
mark - loose life and start over 
apogee - toggles between 16 colors and normal 
gunhed - receive every weapons w/ 100 rounds of each and 5 rounds of TNT 
doom - makes it harder to destroy enemies and collect ammo 
hooker - takes you to the bonus stage after finishing the current level 
hocus - teleports you, provided there's an enemy below or above you 
bad - gives you the hip-hop bird 
sable - gives you super sonic speed 
cstrike - gives you the air board 
bouf - temporarily invincible 
ken - exits game