Cheats:
During gameplay, press:

PIHAMMER - 999 Weapons
PIEXPL - 999 P-Bombs
PISKIP - Next Level
PITIME - 999 Sec.time
PIBETA - Godmode

Level       codes:
Level 06 - 48814
Level 11 - 62615
Level 16 - 55935
Level 21 - 44933