Even easier: I have the AUD (as well as Euros and CAD) rates in Bitcoins on the front page of my site (see sig).
The rates are updated every 15 minutes.
Alternatively, Google has a feature that calculates currency exchange rates. You could use that to convert AUD to USD, and then calculate the Bitcoin value from that:
http://www.google.de/q=55.95+AUD+in+USD