[COBRANIP]

To get tire pressures in the ball park, rub some chalk on your sidewalls near the transition from the tread. After a run you will be able to tell how far over the tires are rolling. If they are rolling too far over (rub chalk away too high on the sidewall) then you need to increase tire pressure.
Good luck and HAVE FUN.

P.S. Most good autocrossers will be more than happy to give you advice and tips....so at the course, don't be shy.