Get Bronze Medals or better in all 10 standard missions.
Get Silver Medals or better in all 10 standard missions as well as the first 2 secret missions with the Millennium Falcon. (Death Star Escape and Asteroid Field)
Darth Vader's TIE Advanced X1 Prototype
Get Gold Medals on all 15 missions.
Complete Tatooine Training in its entirety at all 4 times of the day. That means no red can appear on the mission results. You can set the GameCube's clock by holding when it starts up so you don't have to wait until morning, afternoon, etc. You can't use the ship until you complete the game though.
You need to get this twice in Imperial Academy Heist. During the night, avoid all the sensors. When the canyon forks, take the left road. You'll see a cutscene telling about an Imperial Facility there. Fly up to it, and you'll see a TIE Fighter pilot near the right side of the station. Kill him, and a symbol will appear of the fighter. Switch craft, and steal the shuttle. Instead of the mission ending where it should, continue to fly back to the station and pick up your pilot to end the mission. During the day, ionize all the sensors. Then, turn around and fly over the mountain range. To your left, there's a large canyon with a single sensor dish. If you turn on your targeting computer, there's a TIE parked next to it. It will get up and start to fly away. Shoot a charged ion blast at it, and it will change directions. After landing, there will be a rebel symbol over it. Change craft, and finish the mission as normal.
The TIE Bomber is not playable.