check out scca.org.
but autocross is set up in a very large parking lot, like at a stadium or something like that. the cousre is made up of oragne cones set up to make very hard turns. speeds rarely reach above 70mph and only one car is on the course at a time. you are timed from the time you go until you cross the finish. an average run is around 40-70 seconds.
here is a map of one autox event. http://www.team-integra.net/forum/display_topic_threads.asp?ForumID=4&TopicID=7254&PagePosition=1