At the main menu, choose "Options," then select
"Bonuses." At the Bonuses screen, choose "Enter
Cheat Code." Input the corresponding passwords 
to unlock the following cheats (if you entered 
the password correctly, it should appear on the 
Activate Bonuses screen). To use the Nitro 
button, once it's activated, simultaneously 
press and hold X and L1.

These cheats do not work in Championship mode.

705 Springs: VANISHING
Chrome Cars: T2
Exploding Kerbs: KERBKRAWL
Extra Power: GRUNTSOME
Low Gravity: EUROPA
Motion Blur: ETHANOL
Nitro Button: GLYCERINE