If you're setting up Windows 8 on a new machine, you'll be offered an 'Express Install' option that uses common settings. That makes the process faster, but you'll need to be careful: for at least some versions, Express Install will set the US as your location rather than Australia.
To avoid the issue if you do spot it during Express Install, either skip Express Install and change the region when you're asked during installation, or alter the Region settings after setup (search for Region from the Start screen and look in Settings). Changing your region to Australia should automatically change your language to English (Australia). You might prefer to switch to UK English, since that changes spelling in Windows dialogs and will largely match Australian preferences.