I've been autocrossing for 5 years now. The place to go is Devens airfield. Multiple clubs run there. BMWCCA, NER, Miata club, SVT club, SHO club, probably more... I run with the Boston BMWCCA.
Various websites which will give you more information and how to sign up:
www.ner.org
www.boston-bmwcca.org
www.svtoa.org
This is a pretty good intro to read about autox from tirerack.com:
http://www.tirerack.com/features/solo2/handbook.htmBasic info about rules and what car classifications:
www.moutons.org
..though this is not updated as of a few years ago so if you want the most accurate info, refer to the www.scca.org for official rules
If you have any questions about autoxing, I'm your guy to go to. Autox has been gaining popularity and filling up fast in the Boston BMW club. I'm suprised more of you guys don't try it. It's an extremely low budget way to use all your cars for what they were made for... driven hard!