Under the options menu, enter DARON to unlock everything.
Bizarre Controls
Enter JARJAR on the code screen.
Full Screen Cockpit
Enter CONVISTA on the code screen.
Hidden Snowman
In the Mount Merakan mission near one of the ore refineries there are some little huts. If you destroy all of them and look under them one of them has a droid making a snowman.
Invincibility
Under the options menu, enter SOLID to unlock eveything.
Invincible Craft
Enter ARTOO on the code screen.
Republic Gunship
Achieve the bonus objective in Act 3 Mission 5.
Sabaoth Fighter
Achieve the bonus objective in Act 2 Mission 5.
Slave 1 ship
Achieve the hidden objective in all missions.
TIE Fighter
Achieve the bonus objective in Act 1 Mission 4.
Unlock Everything
Under the options menu, enter LONGO to unlock eveything.