ShellShock: Nam '67 cheats and cheat codes for Playstation 2

Enter the following button combinations in the "press start" screen:

Add weapon:
Press Up, Down, Left, Right, Circle, Square, Up, Down, Left, Right, 
Circle, Square. Pause the game to bring up the "Add Weapon" option.

Unlimited ammunition:
Press R2, R1, Triangle, L2, L1, Up, R2, R1, Triangle, L2, L1, Up

All missions and images unlocked:
Press L2, R2, L1, R1, L1, L2, L2, R2, L1, R1, R1, R2

God mode:
Press R3, L3, Right, Left, L1, R1, R3, L3, Right, Left, L1, R1 

Play in psychedelic mode:
Press Up, R2, Circle, Left, Triangle, Square, L2, L1, Circle, R1 

Bazooka:
Press Up, Left, Down, Right, R2, R1, L1, L2