Go to Options/Passcodes and use the
codes from the list (you will hear a
short click if the cheat was accepted).

GPAYQWAJ  All regular levels
JHGNRGAS  All regular and bonus levels
FMRYLDAD  Dark Side Level
EOWXZGAS  Development Team Photo
DIWMZIAR  Show Credits
HRDTOKIL  Advanced Shields 
RQORACAQ  AAT tank (some levels)
JOBXXFAI  Art gallery in show room
RECTVBAH  Concert hall in show room
FMRYLDAD  Dark Side bonus level
UYCZNCAX  Double secondary weapon
CXSJMIAA  Expert mode
ABVUSEAY  Guided missiles
LFZWKXAA  Infinite lives
FRBPTDAY  Sith infiltrator (some levels)
XFIIYBAY  Swamp speeder (some levels)
NIZWAGAO  All Naboo side ships