Instructions
Exit the game if it is running. Navigate to the website with the stunt track that you want to install for your game. Websites such as RustyFX and RaceSimulations have a selection you can choose from.
Right click on the file after the download completed and select "Extract All." When the installer asks for a destination, specify the "Tracks" folder inside the folder where your copy of the game is currently installed. If you used the default install path for example, it would be "C:\Program Files\Papyrus\NASCAR Racing 2003 Season\tracks."
Start the game and you will find that the stunt track you have downloaded is automatically available to play.