Hey mate.
First of all you need to be a member of a CAMS affiliated club, such as SAU Vic. You can join for $70 first year and $50/y after that. See this thread for info on joining. http://www.skylinesaustralia.com/forums/Sa...ber-t60590.html
You will also need to get your cams L2S License - think it's about $95/year (from memory last time i renewed). See here for the form: http://cams.com.au/downloads/paperforms/20...Application.pdf
Once you have these 2 things you can go to any club level track day you want. Plenty are run by different clubs. WRX Club, HSV Club, PIARC Club, MG Club etc...
We (SAU Vic) run our track championship at WRX days. See this link for more info: http://www.skylinesaustralia.com/forums/20...-C-t203667.html
Next SAU day is on 1st June at Sandown. These days cost around $150 give or take.
As for what has to be done to your car, not a whole lot. You will need a fire extinguisher mounted in cabin (About $20 from kmart, autobarn, etc...) - I mount mine behind the passenger seat under where the legs of a rear passenger would sit. You also need pants, long sleeves and covered shoes. And of course a Helmet (ADR approved).
Also make sure your car is in good condition - ie no oil leaks, working brake lights, all simple stuff that you should have sorted on your car just to drive it on the street
See this link for more info about other events SAU Vic runs for its members:
http://www.skylinesaustralia.com/forums/20...en-t198251.html
If you want to have a look at some Club lap records and past motorsport championship results. Check these links:
http://www.sauvic.com.au/lap_records
http://www.sauvic.com.au/motorsport_championship
Hope this helps