I"m not sure how this thread got to all these posts about WW 2 etc on this page but I will add to it by saying a large scale and successful invasion of Australia by Japan in WW 2 would have been militarily and logistically impossible. Period.
If they had succeeded in capturing all of New Guinea They may have later been able to put relatively small numbers of troops ashore in a few select places on the northern coasts maybe to try and attack /capture Darwin for eg, it being the largest "city" north of Brisbane at that time or far north Qld coast but that would have been it.
The biggest result of any localized battles, regardless of outcome on a tactical level would have been one of widespread "fear and panic" amongst the overall Aust population that a "Jap invasion" had indeed begun due to the widespread lack of reliable "news" and intel in those days and the general British prejudice and superior attitude to the capabilities of the Japanese of the period as was seen after Pearl Harbour and subsequent Japanese invasion of SE Asia and the fall of Singapore and then all of Indo etc.
If anything had occured and Australia had fought fiercely as they did throughout the war as opposed to just finally surrendering as the British did in Singapore and taking 1000s of Aussies with them thanks to being outsmarted tactically by the Japenese attack force then the Japs could never have succeeded.