Cheat: Unlock All Weapons
While playing, input this code to unlock all weapons: hold L2 + R2 and then enter Right, Right, Down, Up, Left, Left

Enter the following codes from the cheat codes menu, which can be found in the setup menu.
Cheat: All Boxers
Start, X, O, Square, Square, R1, R1, Square, O, X, Start.
Cheat: Conversation Mode
Start, R1, X, O, Square, R1, R1, R1, Start.
Cheat: Intercontinental Mode
Start, X, X, X, O, O, O, Square, Square, Square, Start.
Cheat: Scrap-Yard Scene
Start, O, R1, O, R1, X, X, Start.
Cheat: Double Speed
Start, R1(ten times), Start.