Run a few events first and make sure you're into the sport before you start spending a bunch of money. In other words, work on your driving skills first.
Remember to add air to your tires and get there early so you can spend time walking the course and getting to know the folks you'll be racing with.
Most experienced drivers are pretty good about giving rides and riding with the newer drivers. So see who's good and don't be shy about asking for advice and pointers on your driving.
Once you've decided that this is the sport for you and your ready to start spending some money on your ride...go get some good tires!