Various Codes
Before the "Now Loading" screen with the bird logo comes up, press and hold R1+O. This will change the "Now Loading" screen to bouncing CD's. Now you can enter any of the following:
Change your own plane color - While the bouncing CDs are showing, UP, DOWN, LEFT, RIGHT, UP, DOWN, LEFT, RIGHT, then R1. Watch for a Namco character at the lower left for confirmation.
Change wingman's color - Press RIGHT (keep it pressed) and press START 10 times. Look for confirmation again.
Play a short hidden game - Press UP, LEFT, DOWN, and RIGHT. A small character icon will appear in the lower left of the screen. Now the next time there is a loading game, don't press the R1 and 0, and the game will pop up.
999,999,000 credits - Press Down, O, T, T, T, O, T, O, T, then press O+T simultaneously twice and hold both buttons down after the second press. You should see a Pooka from Dig Dug in the corner of the screen. Start the game and you'll have 999,999,000 credits!
Extra wingmen - Hold R1 and press START 10 times. Continue to hold START after the 10th press.