First, go to the "SYSTEM CONFIGURATION" change the time to "2:55am". Then, go to Silver City go through the Main Entrance take a left then another left go to the top of the fountain there will be a teleporter if you made it by "3:00am"
Note: "SYSTEM CONFIGURATION" is on your PS2, you have 5 minutes.
At the title screen, hold L1 + L2 + R1 + R2 and then press SQUARE, CIRCLE(3), TRIANGLE, X and then press START. If you entered it correctly you will have unlimited everythig and all weapons and upgrades.