At the main menu, select "Features", then select "Create-a-Car". Enter "Seymore Cameos" as a case-sensitive name to unlock all cameo FMV sequences.
Win the Daytona 500 with Kevin Harvick (29 car) to unlock Dale Earnhardt. After winning the Daytona 500, a Thunder Plate will appear with Dale Earnhardt on it. Alternately, go to Lighting challenge and play three of them.
Reach level 16 in your EA Bio to unlock the All-Star race.
Reach level 18 in your EA Bio to unlock the Bud Shootout.
Various other Thunder Plates can be unlocked by uploading your EA Bio from other 2004 EA titles, such as NCAA Football 2004, March Madness 2004, Madden 2004, etc.
Go to season mode, then to "Custom Schedule". You can unlock night races for the day tracks.
Win the race that has a locked version of an alternate night track on the veteran difficulty, 3% race length, and damage on visual only. Repeat this method on all tracks that have a locked version of it to unlock alternate night tracks.
Instead of reaching the EA Bio levels for the All-Star race and the Shootout, just race a season on veteran at 3 or more % race length, damage on visual only, and brake and steering help, and win the races.