heres some cheats that might help:
View Ending
Start a new game on Hard and enter your name as "_Credits". When you start the game you will see the ending credits and a playing tip.
View Designers
After you see the ending with view credits, press START to return to the title screen. From here, hold UP-RIGHT with the control stick and you will see the game's designers.
Debug Cheat
Enter your name as _Wampa__Stompa and start a game. Then select a level and pause the game. Now hold all of the C buttons L and R and Left on the D-Pad and the Control Stick halfway to the Left until you hear a tone and then push it halfway to the Right until you hear the tone and then push it back to the Left until you hear the tone then push it back to the Right until the tone and then back to the Left until you hear the tone. Now pink Letters will appear at the top of the screen use the D-Pad to Select them and press A when you find one you like. (I think this one'll give you invincibility and other options)
Ultimate Cheat
Enter _Wampa__Stompa (the _ designates a space) as your name and make sure the controls are set to default. Start a game, pause, then simultaneously press and hold left-C, right-C, top-C, bottom-C, Z, L, R, and Left on the directional pad. While holding the buttons, move the analog stick halfway to the left and hold it in that position until you hear a sound. Then move the analog stick halfway to the right and hold it in that position until you hear a sound. Repeat the process, alternating from left to right until the words "Get All Stuff" appear at the top of the screen. Press the L and R buttons or Up and Down on the analog stick to cycle through the cheats.
couldnt find any level select cheats tho :-(