Will you accept a driver's license from Australia, or do I need an International Driver's Permit?

Not required but the international license makes things easier.

Ian, i looked this up on Alamo site for you. If the home country license is in a language other than English (or French, for rentals in Canada) and the letters are English (i.e. German, Spanish, etc.) an International Driver's Permit is recommended, but not required, for translation purposes in addition to the home country license.

Thanks Steven!