Enter the following code at the mode select screen (the one that lets you pick between Single Race, Time Attack, etc):

Up, Left, Right, L, Z, R.

Be sure to use the D-Pad for the directional commands. This will unlock all courses in the game, including the outer space bonus stage.

To unlock all the bikes hidden in Top Gear Hyperbike, enter the following code at the mode select screen:

Up, Left, Right, L, Z, R, Up, Down, Down, Z, Down.

Use the D-Pad for the directional commands. A rev sound will confirm correct entry of the code.