Check out this:
The latest issue of Famitsu has an interview with Kazunori Yamauchi for the new Gran Turismo on PS3.
+ They'll release 2 versions for the new Gran Turismo (they use the same "Gran Turismo HD" name of the E3 demo for the product names) for the PS3 soon. Both support online multiplayer.
+ The proper GT5 is going to hit in 2008. GT HD is meant to grow the rich network service before GT5. The online modes are based on the 4 modes in GT4:Online beta (Quick Race/Tuned Race/Private Race/Time Attack) and several other modes are added. The online will be launched worldwide at the same time.
+ Gran Turismo HD: Premium is essentially a GT5 prologue that uses the full graphics power of the PS3. (Pictures show a 3D spectator crowd, very detailed car models with interiors.) The weather changes while racing. It comes with 2 courses (both original and new, city and nature) and 30 cars including new ones. You can buy additional 30 cars and 2 courses (real circuits) later online. This version (or both GT HD, not sure) is a pure driving simulator and almost a tool. You don't get cars in in-game events, you just do whatever you want with games and courses or buy new ones via online.
+ Gran Turismo HD: Classic is what adopts the GT:HD playable demo at E3 and meant to showcase the online aspect. A race is done with about 20 cars. Apparently this version starts with no cars or courses. You download a car for 50 - 100 yen (0.43 - 0.85$) and a course for 200 - 500 yen (1.71 - 4.26$). Over 750 cars and 50 tracks are available for purchase. Users can define race events freely and can hold online race events by themselves.
+ Not all cars and courses are available on the release date, they are added monthly. Some models may be a limited release for 1000 units. New playing modes and tuning parts may be available via download. It's still undecided if they allow trade among users in fear of real money trade.