understand ( and I think I am right) that overseas trained applicants in most states in Australia (exempting Western Australia) who have obtained registration in NZ are entitled to apply for full registration under the Trans-Tasman Mutual Recognition Act 1997. In effect this means that Australia treats NZ as another state for this purpose. so just as if you have registration in one state you can then apply for registration in another state.
By applying for registration in an Australian State vie this route of mutual recognition, it is the registration that gives you grounds for acceptance of your qualification. So once you obtain full registration in NZ - away you go!
If you went through an Irish university you will have completed a four year degree (yes?) so that makes registration in NZ not too difficult. If you graduated from a three year degree then there are more hoops to jump through.
there was a bit of grumbling about this - a fear that too many physios were getting Australian registration by using NZ as a transit lounge and would the process be less exacting than sitting the ACOPRA exam. However, I can assure you by the time you have gone to the trouble of applying for registration to NZ you will have really earned it!
Have you had a read of the NZ board site and one of the Australia state board sites in the state you want to work?