On the 1st January 2012 the import regulations changed which restrict the type of car you can now import into NZ. The regulations do differ depending on which country you are importing the car from, so below I have outlined the basic regulations from the 3 most common importing countries which are UK, USA and Australia.
Cars shipping from UK
Cars shipping from Australia
Cars shipping from USA
Summary
The above points are the basics from the 3 main Import countries, I do recommend that you consult with an Entry certifier here in NZ before committing to a purchase of any car, from anywhere in the world. You don't want to run the risk of having a car which doesn't get compliance here. Worst case scenario: You don't do any research around this; you have spent a lot of money and time on importing a car that you can do nothing with. You will never be able to legally drive it on the road, and you won't be able to sell it for this reason. Please make sure you do the research before committing any money to any car.