Concept Car
In order to get the Dodge Concept Car, which you can't buy, you have to win the British vs US race.
Easy Money
The easiest way to get lots of money later in the game is to race the qualifier for the all nighter. You get $20,000 just for qualifing and it is very easy to do this with the GTO special edition or any other car with good speed/acceleration and handling. It takes app. 1'45" to complete with the GTO special edition.
Faster Acceleration
To accelerate faster, rev your engine during the countdown. Be sure to go from the lowest point in neutral to the hightest point in neutral, and back down to the lowest point in neutral as many times as you can before you go.
Hi-Fi Mode, Bonus Cars and Bonus Tracks
To get all the bonus items in Arcade mode, which include the four other tracks (Autumn Ring, Deep Forest, SSR5, and Grand Valley Speedway), all the other cars (Toyota, Subaru, Dodge, and TVR), the ending movie, and Hi-res GT Mode, you have to beat every single track with each type of car (A, B, and C) under all three modes of difficulty (Easy, Normal, Difficult.)
Hidden Video of the GT Staff
In Arcade Mode, first get the hidden tracks, then, on every track, take 1st place with any car in A,B, and C class mode on Normal setting or higher. Then go to Bonus Items, you'll see "Staff Video" on the menu.
Replay Mode Tip
Are you having trouble beating the license tests? Well, you won't anymore. Go to the replay theater in the main screen, and check out the demonstration movies. They will show you how to beat all the license tests!