In the TDOR directory on your hard drive, go to the PLAYERS sub-directory. In there you will see a file named: TSTRULS. Change the name of this file to <something creative>.pin. For example: Cheats.pin. The important point here is the .pin extension.

Start TDOR
.
At the Main Menu, choose a league or the Practice Race.
At the player screen, type in a code:

Code Effects :

cheat1 -  all vehicles available
cheat2 -  all tracks available
cheat3 -  view all endings
cheat4 -  no collision (must quit out of game to restart collision)
ciggies -  All the ground in the game goes flat