Thanks to your both answers.
Physics and collision: I don't like to re-invent the wheel. I plan to use as much as possible existing stuffs. The problem is to find the correct one. Also I've seen that DLL's are faster than DB code...so.
There is no multiplayer. The server connection is only for saving best time on a web server page. But I've first to create the game ;

The actual problem is how to manage the track ? I've seen so many demos on the site I've downloaded (mainly car game demos) but none seems to manage a real terrain. They are all flat matrixes (and matrixes are slow to manage by DB...)
I've seen there is a .x terrain possible, but since I've never created anything with DB, and I really must start, what's the best way to get started:
The game seems simple: a track, a car and arrow management. Once I've everything working, creating objects around the track shouldn't be as difficult. I know I must manage dynamics and collision....but first I'd like something that moves and see the result I can achieve.
Thanks for help.
Bob