Don't forget you will need a 'visa' or more correctly an ETA which is available on the Australian governments immigration web site. Cost is around $US14. Some other dodgy visa sites out there so be careful you use the correct one.
Only mention this as it appears from the travel forum I frequent that many Americans are unaware of the requirement until the last moment and have applied only to have the ETA not granted in time for their departure. Normally it takes from a few minutes to 24 hours but on occasion manual processing for security reasons takes place extending the approval time, sometimes into weeks.
Hope I am not teaching my grandmother how to suck eggs but if so, i apologise.