At the main menu, hold R and press Black, White, Black, White, Black, White repeatedly until the cheat option appears at the bottom. Then, pause the game and press X to access the cheat menu at the bottom of the pause menu. After cheats are activated, a message will appear in the top right part of the screen during the game. Note: The cheat options can also be activated in online games, but may require the game host to first enable cheat mode.
Just before you get the mini-gun, there is a door on your right. Open it and there will be armor on the other side. You must to step on the correct letters; the order is: S, E, R, I, O, U, S.
In the level when you must defeat Zum-Zum, you must first destroy all of the giant sunflowers so that Zum-Zum cannot regain its life. Once you destroy the sunflowers, you can attack Zum-Zum and kill it before it recharges.
There are several passing remarks in the game about a "Blonde guy taking forever". This a reference to the as-yet-to-be-published PC game Duke Nukem Forever.