Unlimited Lives:
Goto the Main Menu and enter the following:
Left, Left, Left, Right, L2, L1, R2, R1
You can access this cheat during gameplay by pressing start and using the cheat menu.

Infinite Ammo:
Goto the Main Menu and enter the following:
Down, Right, Up, Left, L2, L1, R2, R1
You can access this cheat during gameplay by pressing start and using the cheat menu.