Jester,
I have not seen any Americans be able to do the Australian accent unless they were professional actors. Even English and New Zealanders can't do it let alone Americans.
Nobody speaks like Steve Irwin here, he has what we call a 'bogan accent'. It's the equivalent of the real outback Southern American accent, if you speak anything like Steve Irwin it means you come from the outback, your probably racist and you probably screw your sister.
In Sydney we call that the westie accent, only the poorest white folks speak like that.
This would probably be more accurate for how most of us speak. With a little exaggeration at the end.
http://www.youtube.com/watch?v=KpBYnL5fAXE