You can vote anywhere in australia, or at an australian embassy, consulate or misson anywhere in the world. If you know you are not (or may not) be able to vote on election day you can pre-poll either in person or my mail several weeks before the election (Basically once the candidates are confirmed). My parents were on the sunny Mediterranean on election night and so pre-polled several weeks ago.
These votes are counted last, I.e. only if they could change the outcome of the election.
If given all these choices you still didn't attend to your duty you will receive a fine of about $50.
Strangely enough practically all Australian do conscientiously attend to voting. At the polling places there are the usual rabble who want to hand out "how to vote" cards. Most people have already made up their mind, and either don't want one, or only take the one for the party they so desire.
Of course, deciding to vote informally shows that the person has made a serious effort in understanding the candidates, their policies, and possible decided that they are all bat shit crazy. It is a valid choice. the difference between allowing compulsory voting (including informals) and optional voting is simple. If you decide to vote informally you have still looked at the candidates, and thought about it.
I generally start voting from both ends. I know who goes first, and who goes last. It's the great unwashed in the middle that is so bloody hard to order :-)