GT Hi-Fi Option
Win the 'Gran Turismo World Cup' to unlock the GT Hi-Fi option.
Submitted by Blade. 

Concept Car
In order to get the Dodge Concept Car, which you cant buy, you have to win the British vs US race.
Submitted by York_L_Wilmore. 

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.
Submitted by York_L_Wilmore. 

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.
Submitted by York_L_Wilmore. 

Nissan Nismo 4000GT-R
To get Nissan Nismo 400GT-R you have to get all golden trophies in International A class license.
Submitted by York_L_Wilmore. 

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).
Submitted by York_L_Wilmore. 

Go to: Gran Turismo Info Page | nGaming Home Page.