Unlock Extra Drivers:
     Enter Extra Drivers as your name when you create a driver.

Unlock Dale Earnhardt:
     Enter Dale Earnhardt as your name when you create a driver.

Unlock the Tiburon Speedway:
     If  you  have  a savegame from any other EA Sports 2003 title you
will unlock the Tiburon Speedway track.

Unlock the Tiburon Speedway:
     Another  way  to  unlock  Tiburon  track is to play the lightning
challenges.  One the challenge when you play as Harvick at Atlanta (or
at  least  thats the way it was for me) you will unlock Tiburon track.
This  track  has top speeds at nearly 240 MPH, it is 3 miles long, all
banking, and looks like Talladega, except that you race backwards.

Faster car:
     If  you  have  unlocked  Tiburon  Track and realize that your top
speed is only about 235 MPH, then you can do 2 things.

1. Under car setup, make your car all speed, and not handling. 
2. Turn off auto brake. Auto brake will not allow the car
to exceed 238 MPH.
Note: Tiburon Track has no restrictor plate, so you can change
the downforce.

Unlock new paint scheme:
     Use  a  driver  with  a paint scheme and win a race on veteran or
legend to unlock a new paint scheme.