I made a short tutorial on how to model a race track with round corners, you can see it here:
http://www.oliver.dbspot.com/index.php?section=tutorials&page=track. This is how the levels where made in my alienware competition entry, ETV Racer. So, I hope it helps (and I hope it works, it should work with any modeling program).
The rest of my website is under
heavy construction and theres alot of unfinished stuff on it. Anyway, tell me what you think about the tutorial and the website (i.e. whether either of them work),
Oliver