ok i want to enter in the autocross near my house or in MN but i don't know what would be the best thing to do to get my car ready for racing cause my 84 z28 isn't gonna be to good in the qauter i dunno y but i like raod caorssing better so .. but i don't need a roll cage and anything really expensive so please help

First and foremost make sure everything on your car is in proper maintenance. Good brakes, tires, engine, tranny, diff, suspension, etc...

If you really want to get into competing in points then look over the rules for where you will be running as what class you run in depends on what modifications you do to the car.

Mods that make the biggest difference but won't bump you up to much in classing include:

Tires(+255's on good rubber. R-compound tires will generally make a car 2-4secs faster)
Shocks/Struts(Koni, Bilstein, Tokico,...)
Swaybars(eg. 35mm front)
Rear end gears/posi(at least 3.42's and a better posi like the T2R)
Performance Alighnment

These are some of the most significant mods overall for autox. But make sure your car is running properly first or you'll just make it run even worse after an event.

Find a used set of 16X8s and get Kumho or Hoosier tires (245/45/16). Good shocks would be next.

If you want to stay in stock, make sure the rubber bushings are in good shape. Beyond that you should consult a rule book for what you want to do. Here are an unofficial set of rules: http://mouton.best.vwh.net/sccasolo/Rules/stock.html .

Just go and drive. Talk to other drivers, most will be willing to help and give advice. And most of all enjoy yourself.