There are a number of "hidden" controls in Gran Turismo 4 that will make navigating the game a bit easier.
On the main Gran Turismo Mode screen, press L1 to jump the cursor to Home, and press R1 to jump the cursor to the country of your vehicle's manufacturer.
When looking at your garage in Home, press START to bring up the vehicle settings screen.
When changing your vehicle's settings, press START to enlarge the Engine Power/Torque curve.
At the end of a series race, press START to skip the finish times and championship points screens.
During a replay, press L3 to fast-forward.
During a pit stop, press X to to stop refueling, letting you get out of the stop faster.
With the Driving Force Pro wheel, press any combination of the LEFT, RIGHT, and DOWN buttons on the D-pad to look in that direction while driving.