From the Main Menu, go into Options and then Cheats. You will be warned that
when any cheats are enabled Career mode cannot be saved.

Enter the cheats in the Cheats submission form. If you enter a valid cheat the textbox will blank out. If you enter a fake or incorrect cheat the textbox remains unchanged, and you will hear a sound indicating error. All cheats are case sensitive.

Effect - Cheat Code
Icy Courses - AllIce
Unlock all levels - AllLevels
???? - AllMyPeeps
Rider never crashes - DontCrash
Rider moves faster - FastMove
Low Gravity Mode - LowGravity
Max out rider stats - MaxSkills
Deactivate Cheats - NoCheats
No Collisions with other riders - NoCollisions
Unlock All Videos - ShowRewards
Spin Faster - SuperSpin
??? - TrickedOut

When you want to resume regular play use the NoCheats code to restore your career mode.