Level Skip:

Start a game as usual.Then bring up inventory and move it down to the passport.Open up the passport and go to the last page for exit game and hit Z,

Y, Z, Y, X, X, X, and start.You should hear a confirmation sound.Then exit.But don't worry the game will bypass the exit and show the level complete screen.

Unlimited Ammo:

If you beat the game, you will have unlimited ammo for the weapons you have in any level. Be sure not to select new game otherwise it will erase your progress. Enter the level through the load game screen at the title or while the game is paused in the passport.

Weapons Code:

Before entering the level skip code, (Z,Y,Z,Y,X,X,X, Start) enter the last page of your passport, as you do with the level skip, and press X, Y, X, Y, Z, Z, Z, Start. You WILL NOT here a confirmation sound. Then enter the level skip code. At the start of the next level, pause the game and go to your inventory of weapons. The shotgun, uzi's, and magnums are now at your disposal.