For greater firepower in two-player mode, have one player fly his jet directly on top of the other one. Your firepower will merge, and become faster and more powerful. This works for both the main weapon and the secondary.

Select Settings, then choose the Difficulty option. Press and hold L1, L2, R1, R2 and press Start.

To control the demo hold R2 and you can play the demo just like the regular game.

For unlimited credits, go to the options screen for either game and press Triangle + Circle + Square + X. A new option called "FREEPLAY" will appear.