Unlockable Modes
To enter the notes go to 'Options' and select 'Cheat' and enter the code you want to enable. You have to strum as you press the buttons in the code or if two buttons are indicated they must be pressed together as you strum as they represent one cord. The letters in the code below correspond to the colored frets.
R = Red, B = Blue, G = Green, Y = Yellow, O = Orange
Unlock Everything:
Press GR_BO, GRYB_, GRY_O, G_BYO, GRYB_, _RYBO, GRYB_, G_YBO, GRYB_, GRY_O, GRY_O, GRYB_, GRY_O (because this code uses 4-note chords there will be no sound).
Unlock Air Guitar Mode:
Press BY, GY, GY, RB, RB, RY, RY, BY, GY, GY, RB, RB, RY, RY, GY, GY, RY, RY.
Unlock No Fail Mode:
Press GR, B, GR, GY, B, GY, RY, O, RY, GY, Y, GY, GR. In this mode you won't fail any song regardless of difficulty setting (doesn't work with Career mode, Online or Top scores online).
Unlock Easy Expert:
Press GR, GY, YB, RB, BO, YO, RY, RB (the timing window becomes larger for hitting notes, doesn't work in Single career mode).
Unlock Bret Michaels as the Singer:
Press GR, GR, GR, GB, GB, GB, RB, R, R, R, RB, R, R, R, RB, R, R, R (using this code on Online gameplay has been known to cause a glitch).
There are more cheats than this so use google and find some more. I know two of the "missing" cheats are called Performance Mode and Precision Mode (note: they both make the game harder). Well I know there are more on the ps2 version but not sure about the Wii