Here are the level codes:

JAGUAR
BANTHA
TOHOLD
COMBEL
SHIVA
PICOLO
ANTIC
KASYYK
FUGU
NOLAN
SARLAC
CAPSUL
ARTHUR
MAENOC
ZZZAP
SHIRYU
SULUST
MANIAC
RENDER
NEPTUN
NO WAY
BELUGA

Some say the password PIXEL kills guards ....

There's also a handy bug in it:

Walk as close as possible to a wall, or a closed door you want to go through. Turn back, start running away and immediatly, turn back while running, towards the wall. If you release the [Shift] fast enough after starting to run, you go thru the wall. You will have to play around with that [Shift] key a bit to get the hang of it