Xtreme Sports

Unlock secret course:
Play in easy mode, and choose the Himalaya track. Go to the "skeleton"
tunnel, and turn to follow the alternate route to the left.
Pick up the medallion to play on secret ATV course.

Unlock Hard mode: Win 1st place in the easy mode.
Unlock Expert mode: Win 1st place in hard mode.

Medallion:
Play in easy mode, and select Maui. Towards the end of the
snowboarding race, turn to the left on the last grind rail.

Unlock Extra Tracks at the main menu:
Earn all the medals on each level