I''m totally confused about way how to represent a map of car racing lap to make the programming the intelligence of cars drived by PC easier. Can you help me?

Try :

http://opensteer.sourceforge.net/

They represnet path as a series of vertex and radius. This and some simple collision code should be what you need.

Opensteer is using the MIT lisence, so it''s available for commercial applications too.

Good Luck!

-ddn