Pr-requisite? No, anyone* can autocross. If you never have before, sign up for novice. For the Practice, it doesn't matter, just a practice, but for the Sunday event it will.
*you do need things like, a car, and a valid driver's license.
Check out these sources for info getting started.
http://www.nwr-scca.org/solo/Start.htm
http://www.wwscc.org/so-how-do-i-get-started.html