Access All The Cameo Videos
Go to Main Menu, select Features, then select "Create-a-Car". Where you're asked to type in a name, type in:
First name: Seymore
Last name: Cameos
Make sure you have a capital S and C since the name fields are case sensitive
How to unlock peoples other cars
The first thing you do is go to race now. Then when you get to the race now settings set it for one player, and set the difficulty for medium. Then pick the driver that you want to get their cars for and win the race and you will unlock one of their cars. note; you can't keep doing the same track with the same driver or else it won't work.
Get Paint Schemes and tracks
Set the race mode to either 3 5 10 25 50 75 or 100. Then set it on veteran or legend. Then pick the driver you want to unlock a special paint scheme for. Then select the track you want to unlock. Win the race and you now have a new track and car.
Dale Earnhardt Sr.
Win at Daytona 500 in Season mode and you'll unlock Dale Sr's Bass Pro Shops car, Silver car, Black 3 car, Coca Cola car, and Legacy car
EA Sports Bio
If you have previously played a EA sports 2004 game and have your EA Sports Bio saved, whatever level you are in will be the level you are in in Nascar Thunder 2004, so you can also unlock Thunder Plates