Forget Australia it's all desert dude, no green stuff.
If you're single(ish) theres hotter women in Australia, theres a few hotties in New Zealand but most are average by International Standards and are far too demanding
If I had to holiday in NZ I would strongly recommend Taupo, then drive to Hawkes Bay (Napier in particular) from Taupo then take State Highway 1 via Dessert Rd to Wellington and then tour the South Island a little bit.
You have to see NZ by car; planes, trains and buses just will not do it justice
Taupo you just missed the A1GP that was a week ago; but still theres the lake, probably pay to get a hold of a boat and spend a few days there
Some decent fishing in Hawkes Bay and a whole lot of vineyard's out that way
Then the drive from Taupo to Wellington is pretty cool, but don't bother with the Army Museum cause it sucks; but stop and ask them for the direction to the Air Force Museum which is about an hours drive away. While on the topic Te Papa in Wellington is worth having a look in and so is Auckland Museum.
Auckland is near the top of the North Island, Taupo is in the middle with that great big lake on the map and Wellington is the bottom of the North Island
If you're going to be around Auckland I would highly recommend a trip to Coromandel in particularly 'Hot Water Beach', Piha is pretty decent and might pay to check out Miruwai and within Auckland itself I would say check out Long Bay Beach
I've never been down to the South Island but I've heard it's pretty cool with the mountain ranges n stuff
You would want to set aside at least a week for it if you drive one way and fly/train back