I have it, and am currently working myself through it. Like it a lot.
If you get it (or have it), after you build up a halfway fast car, go to the "special conditions" area or whatever its called. Win the first race there and receive a really fast 700+ hp car. Use that car to win the second race in the special conditions area, and receive a car that can be sold for $300K. Doing this over as necessary gives you unlimited money to buy whatever cars you need for the rest of Gran Turismo 4.
best regards