From GTPlanet Game Guides

I added the following 4 cars:

Dodge Neon ACR

- This is a four-door version of the first generation of Dodge Neons. It has the same specs as the coupe version. Of course, I noticed it was missing form the game, because it the one GT2 car that most resembled my own car.

Fiat 500R

- For those keeping track, this is first Simulation Mode car I ever bought. It's one of three new cars (Diahatsu Mira TR-XX, Midget D-type) you can buy with the initial 10,000 credits.

Mercedes-Benz CLK Race Car

- This is one of two "original" hidden cars in the game; it's not the CLK-GTR or the so-called CLK DTM. This car is a creation by Polyphony Digital; nobody knows for sure why this car was hidden from the game. You need a GameShark or equivalent device to buy the car, using the right set of codes, You can also buy it from another memory card, if someone else has a copy of this car. It's a hidden car no matter what version of the game you have.

Volkswagen Polo

- The other hidden car in the game. Again, nobody's really sure why this car is not in the game; however, you may actually race against it in the Event Generator. The only way to get it is just like the aforementioned CLK Race Car. It's a hidden car no matter what version of the game you have.

Other hidden cars

This is a good time to talk about hidden cars. Depending on what version you have, some cars are locked out and replaced with others. Usually, you need to code your way into buying these cars.

Honda versus Acura

Cars like the NSX and the Integra are sold as Acuras in ther North American markets, so naturally, in the game you have to buy them at the Acura dealer if you have an NA version. This means that some of the race-mods for the NSX/Integra are available if you buy the Honda versions. There's also two additional versions that are unique to the Japanese GT2 game; the Integra Type-R 98 Spec and the NSX Type-R '92. You'll notice the ITR can be used in some of the license tests in the NA version.

Esso versus Exxon

Some of the Peugeot race-mods and the GT-One Race Cars use the Esso sponsorship instead of the Exxon brand of petroleum. Otherwise, the cars are identical.

Infiniti and Nissan

The Inifinti G20s ('91, '96, and '98) are called Nissan Primeras. No different.

Lexus and Toyota

This is where is gets unusual: The Lexuses (Lexii?) are sold right alongside the Toyota counterparts. Easy enough, but the engines vary. The Soarer (turbo 3.0L engine), the SC300 (NA 3.0L engine), and the SC400 (4.0L NA engine). All are slightly different. The Aristo '97 (turbo 3.0L engine), the GS300 (NA 3.0L engine), and the GS400 (4.0L NA engine). Again, slightly different. And then Altezza and IS series. There's the Altezza RS200, the Lexus IS200, and the Lexus IS. Confused yet?