Unlimited Lives:
In the password screen type "iamdolly"

B-Wing:
star : Enter this and you can fly a B-wing.

AT-AT:
AT-AT : Enter this and you can drive an AT-AT

Advanced Missiles:
Enter TOUGHGUY as password

AT-ST:
Enter chicken to play as an AT-ST

Tie Fighter:
Enter "wookiepelt" to fly millennium falcon
Enter "goodguytie" to fly the tie fighter.
Then when onto the area where you select your craft, go to the millennium falcon (having already entered this cheat) when the panning camera stops moving, pull back on your stick, or press down arrow on the key board. The game will then pan round the back of the millennium falcon, let go of the stick/stop pressing down, and hey presto there's the Tie fighter. If you look carefully when you are in front of the falcon before you pull back on your stick you can just see the tie fighter sitting there.