Pull out Lightsaber Underwater- Just press Start, highlight weapons and pick the lightsaber.
Cheat Menu (Possibly Japanese Version Only)- At the title screen press and hold L1 + Select and press Triangle to get the cheat menu with various options.
Get All Weapons- Press L1, L2, R2, X, R1.
Skip Levels- Press L1, L1, R2, R2, X, L1, R1.