Unlock All Missions and Weapons:
At the Main menu enter the following to unlock all missions/weapons:
L1
R2
L2
R1
R1
L2
R2
L1
Invincibility:
For your car to be invincible pause game play and enter the following:
L1
L1
L1
R2
L1
R1
R1
L1
R2
Repeat the code again to revert to normal.
Infinite Ammo:
For infinite ammo pause the game and enter the following:
R1
L1
R2
R2
L2
R1
L1
R2
L2
Repeat the code again to revert to normal.