At the Main Menu, go to Options, go to Cheats and enter.

Code	Effect
CARSHOW	Unlock all Paint Jobs for Non-Lightning McQueen Character's.
EVRYBDY	Unlock all Characters.
GOLDKEY	Unlock all Story Mode events.
GR8MODS	Unlock all Custom Kit Parts for Lightning McQueen.
SLVRKEY	Unlock all Arcade mode events.
STICKERS	Unlock 3 Modified McQueen's.