Use the following codes while playing:

FIREWORKERS - Infinite bullets
INSTRAVELOUS - Type wxx to go to any level (w01 - first level, w00 - the last one)
MEGAMASSIVE - Infinite gravity
ZOMBIEBALLS - Infinite lives

Note: When a cheat is active, there are no end level 'Keys', also no High score entry, and the ending sequence is not shown.