try this one
http://www.oman3d.com/tutorials/3ds/wheel/
and this one for a destructive car(its not a car but the idea is the same)
http://www.tysonibele.com/Main/Tutorial ... namics.htm
and here you have a tut for beginners in reactor
http://www.youtube.com/watch?v=TbVIu61fQcA
(and the next time try to google about it this links were just in the first 5 that appeared)