Cheat
In the options menu, highlight exit and, while holding down buttons A, B, and C, press the start button. when you press it, you will see "cheat enabled" under the picture. exit out, and when you see the screen which tells you what course you are on, press the mode button to change the course. the only thing is that you need a 6-button controller for the mode button. You can now choose between all 24 courses.
Level Skip
Select the one against one icon, then select any player. Now, if you have a controler with a MODE, and X buttons, play until you see the screen that tells you what level you are on. Press the X, and it will take you back levels. And MODE will take you foward levels.