Hello swagman, no shock that you are from Australia going by your screen name.

I do not know the answer but I can tell you when Italians friends in Italy have come to my home state, California, I inquired with our local police dept. and our State of CA Dept. of Motor Vehicles and both told me that all they needed was their Italian drivers license.

I would suggest that you post your question on the Australian Board here on Fodor's. NeilofOz has driven throughout the US more then once and he could certainly advise you I would think. Have a beautiful time in Hawaii, I always think of it as our jewel of the US.

Since an IDP is a language translation of a foreign license there is NO reason an Australian would ever need one in another English speaking country. Just as one would never be required of an American in the UK or in Australia. What would they translate?

Well, there is at least one reason why an Australian might need an international driving permit. I quote from the FAQ section of the web site of the U.S. consulate in Australia:

"Q: Do I need an international driver’s license to drive in the United States?

A: An International Driving Permit serves as proof of validation of your Australian state license and as another form of photo identification. However, you must also carry your Australian state license. Some rental car agencies require an international driver’s license as part of the agreement. Contact your local Australian motoring association for more information."

I don't think that was especially well worded. It probably should have begun with the one-word sentence "No." And then that place where it says "international driver's license" at the end really should have said "permit," I think. But there you have it. Maybe best to call your rental company before departing just to make sure they're okay with the Aussie license?

Here's the U.S. Embassy in London's version of the answer:

"Motorists visiting the United States from countries which have ratified the Convention on Road Traffic (the Convention has been ratified by Great Britain), may use their own valid drivers licenses to drive in the United States for a period of up to one year. Provisional licenses are not acceptable."