I've been autocrossing for almost 2 years; here's what I've learned:

1) it's a BLAST

2) NEVER judge a racer by the size of his engine. I've beat corvettes by 10 seconds, and I've also had my ass handed to me by 1st-gen HF CRX's. My car is a stock 91 CRX Si.

3) you won't learn anything by just watching, except maybe who is who, and what people will tell you about their experiences. The only way to get into it is to..well, get into it. Show up, pay for your runs, and get out there.

You'll really learn a lot abotu your car when you start autocrossing. I highly recommend driving with an instructor the first few track days. Don't let them drive, but have them ride with you and give pointers. It helps a lot. Don't get discouraged if you don't do well right away. It takes lots of practice and constant repetition. I'm still a terrible driver because I can't race consistently while I"m in college. Just get out there and enjoy it.

Oh, and you do not need yoru own helmet. The SCCA provides loaner helmets. You will not be allowed to race if your battery is not secured (sounds silly, but lots of people don't use tie-downs), or if you have loose stuff inside the car. The tech inspectors will walk you through all of that. Just show up ready to learn, and have fun with it.