To get extra fighters:
1.cone headed man with purple saber (forgot name) successfully complete all the traing missions using adi gallia.
2.captain panaka: complete the game with obi wan konobi
3.play as darth maul:complete the game with qui gonn jin
4.play as queen amidala: complete the game with adi gallia
5.play as a battle droid: complete the game with mace windu(there are 2 droids 1 without a gun and the other with a gun,to get the other one complete the game with the man with an orange saber).
Note: you can unlock 2 at a time on 2 player u dont get anything for completing the game with unlocked characters.
If u finish the game with all the characters and the hidden ones you unlock a secret level where u play as one of them rolling droids, u have to kill soldiers with jedi's as the bosse's!!
Really cool and fun to do.....!