Enter these cheats during gameplay followed by ENTER 

Code                 Result
---------------------------
deadlineisnear     - Finish level 
diediediemydarling - Game Over 
glitteringprizes   - All PowerUps 
moremoreweapons    - All Missiles 
showmetheweapons   - All Weapons 
igonnaliveforever  - Infinite Lives 
invulnerability    - God Mode