A few versions of this game was released with different passwords in each. So it could well be the case that the following codes may not work on your copy of the game. There's no harm in trying however.
LEVEL 1 ----- LEVEL 2 ------ LEVEL 3
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----------- | "ZAIVIT"---- | "BOOMAN"
"GLYCKEN"-- | "ZIOMAL"---- | "BINNON"
"SEEPPUN"-- | "NOIBBAT"--- | "CLOINAL"
"MEPEL"---- | "VIANEN"---- | "FLESSAR"
"PLOOTTIT"- | "CLIENNUNG"- | "TIGFIN"
"WAMAL"---- | "WAIVOR"---- | "TOKEN"
"CLOOPAN"-- | "GLEALLOG"-- | "SAKUG"
"GIAPOG"--- | "MEFFAN"---- | "TAIGGAT"
"ZULLAR"--- | "SIEDDER"--- | "CLYFIT"
"BEGGEN"--- | "TOUKER"---- | "SIPUG"
LEVEL 4 ----- LEVEL 5 ----- LEVEL 6
-----------------------------------
"GEABBAR"-- | "WYVAN"---- | "SLAINUN"
"TAPPER"--- | "SLYPPIT"-- | "PLEAMIN"
"VOASSOG"-- | "FLOGGAL"-- | "GYVET"
"GIVIN"---- | "VENIN"---- | "TEETTAL"
"TIAVER"--- | "DRUTTEL"-- | "BOACKER"
"PLOIDDOG"- | "GLIETTUG"- | "BOICKEL"
"NEABBAN"-- | "FLYNNEL"-- | "PLOAGOG"
"PAIBBIN"-- | "MIOSSAT"-- | "FLOUMUN"
"BYMEL"---- | "DROADDAR"- | "WOISSAN"
"SLOOVOM"-- | "BOUTTOL"
If you press the 'Help' key during play will skip levels. Again, this may not work on all copies of the game as different variations were released.