At the "Press Start" screen, hold L2 + L3 + R1 + Down + Square + Circle (in order). All skiers (including Skier X), costumes, and skis will be unlocked.
Game Shark Codes
Master Code (Must Be On) 0E3C7DF2 1645EBB30C072E5F F8A1E387
Infinite Time 3C3BE167 BAF6441E
High Score 3C315B13 42FCFEFE
Unlock All Levels 3DEB6303 F8FCFEFE3DEB614B F8FCFEFE