What John said, but I will add this:
It was said to me at my first Autox event: "It's the most fun you can have with your clothes still on."
You asked if you could be competitive. I'ld say at first, no. Learn your car. I know it's hard to do in Minnesota, as I grew up in Anoka. Learn how to drive your car. Learn it's limits in every situation. Good thing about Minnesota is, if you don't mind driving the stang in the winter, ice'd over parking lots are a great place to learn where traction ends, and how to cope with the car out of control. I learned how to drive in a 5 speed charger ('86 FWD) in the middle of February.
The first season, if you haven't already modded your car, leave it stock, as already stated. Trust me on this one. You won't REALLY be competitive at first, and switching to E Street Prepared off the bat would just discourage you more. The modded classes are normally dominated by cars that can handle better than yours, and driven by people with more experience than you. Not trying to offend anyone, because we all started as beginners. Its those of us that didn't get discouraged the first few events that became good drivers...
Give it shot, I'm sure you'll be hooked!!!!
Two last pieces of advice:
1. Most importantly- HAVE FUN!
2. Drive it like you stole it!
And if those fail, read the bottom of my sig!