Netflix integration is one of the big selling points for the Apple TV in the US, but it isn't an option for Australian buyers. However, you can access the streaming rentals service with a little clever hacking.
MacTalk forum poster Steeley walks through the process he used to set up his new Apple TV to act as if it is in the US. The process isn't especially fiddly, requiring you to set up a US iTunes account and then use a special DNS service to fool your system into thinking your machine is based in the US. The method described uses a paid-for proxy; while there are free solutions that perform similar tasks, those often can become problematic.
It's not a solution everyone is going to want, but if you don't like the content restrictions on local streaming media services, it's worth considering. Hit the post for full details of the setup, and check out how to jailbreak your Apple TV for more customisation options.
How I set up my Apple TV with Netflix [MacTalk]