One (PSX)

Enter the following codes at the Password Screen:

Level select:
HEVYFEET

All weapons:
MAXPOWER

Debug mode:
HEYBUDDY

No "Pause":
THEPRESS

Level passwords:

2 -- DIYGIXRA
3 -- KCSVJTJB
4 -- RWLKLPBC
5 -- YQFZMLTC
6 -- FLZNOHLD