It's true!  You can 'hire' a rental car for free in New Zealand.  Auckland in the north of the North Island runs out of rental cars regularly, so campervan companies provide free vehicles in exchange for you transporting them back to the main depo.

So, if you're coming to New Zealand and want to get a good look at the country, fly into Christchurch or Queenstown in the South Island and drive your way north to Auckland.  The packages typically include free ferry ride across the Cook Strait separating the South and North Islands, and free insurance. 

See www.transfercar.co.nz to see what's available now.  I took a look this morning and there is one five seater van in Queenstown and 23 vehicles of various shapes and sizes in Christchurch available. 

Make sure you get your international drivers license and make yourself familiar with driving on the left hand side of the road.