Allan,
you can download Plane plotter from the following link:
http://www.coaa.co.uk/planeplotter.htm
Go to the PP user group (
http://groups.yahoo.com/group/planeplotter/) and download the files for Australia so you have proper Australian Maps. I normally use the VATPAC ones because i'm used to seeing a radar screen like that.
Have a look around the program and make sure it works, then purchase the software via their website.
Once you get the code, you'll be able to start "sharing" so you can see other aircraft.
You should now be able to see all aircraft within Coverage and have ADS-B