Hi there!
I had the pleasure to fly down in NZ two years ago. I had my German PPL converted to a NZ PPL within about five days including the paperwork. We had to do a couple of patterns with an instructor, some airwork and a checkflight of about 30 minutes. Also a short theoretical exam which was no problem at all, very basic stuff only. The whole paperwork went to Auckland and our license arrived three days later. You can have it sent to the Aeroclub.
Those people were very friendly and competent, they have a lot of planes (mostly PA28s) and enough personnel for you not having to wait too long. Also the Friday afternoon beer call was a lot of fun!
I donīt have an email-adress handy now, but Iīm sure youīll find that one on the net!
Enjoy flying down there, itīs really a great experience!