Cheats:

 Type them in in the password menu:

 FRONT242       Start with more lives, weapons, etc....
 MOREMORE       More lives, weapons etc also in the other levels
 EXCITEME       Level 5 ( ... MOREMORE)
 INSIDEPC       Gag level 4
 STARBATT       Bonus level 1
 PACMAN95       Bonus level 2