Enter the "Create Player" option from the main menu, then enter one of the following names to activate the corresponding cheat function:

All cars have 933 physics - yraGyraG
Cops on most tracks in quick race mode - fuzzyfuz
Destruction Derby mode - Smash Up
Double speed in single player mode - freewill
Drive with Rally physics - Dakar
Heavier cars - fetherw8
Small R/C cars - Gulliver