Is it possible for me(a U.S. Citizen) to register to vote in 2012 election? While living in Australia?

Hi, I turn 18 this year september, and was wondering if I would be able to vote next year for the 2012 Presidential Election, I'm a U.S. Citizen, and I've been living in Australia for 9 months, how do I go about in this, I really want to vote next year, or do I have to go back to America, or, can I go to the U.S. Embassy at Canberra? Help please