Cheat
For all courses, boards, and 1 extra boarder:
D= Digital Stick
A= Analog Stick
C= Yellow Buttons

At the Main Menu, press:

Ddown, Dup, Adown, Aup, Cdown, Cup, L, R, Z, Aleft, Cright, Dup, B, Aright, Cleft, Start

You know it works when you hear a "Yeah!" after pressing Start...

Codes
Type in the following codes during gameplay:

Hold A, press Down rotate the stick 360 degrees twice and hold Down, now you can release A-Do jam's moonrock
Hold A and push Left, Right, Neutral Position, Up, Down and hold Down and release A-Do nancy's limbo.