www.lfsnz.com is a great site with plenty of organised races and low ping servers. We have a pretty large contingent of Aussie racers joining in, and every one from super fast aliens to LFS first timers racing as well. New 2011 series are under discussion as we speak so why not pop on in?
Another good Aussie Server is Monday Night Racing, those boys meet up every Monday Night, with Qualifying/Racing starting at 9pm, the Endurance FOX race that just went was great, Qualifying started at 9pm, with Racing underway by 9:30, the Race finished at 10:30pm, meaning that if your a tradie that starts at 8am, your still going to bed at a reasonable time for work if you work the following morning.
EDIT: Forgot to add that you need to join the forums, register with them, express your interest with whatever series they have going, and then on the morning of racing, they'll send you an email telling you the server password for that night, along with other details, etc etc etc.