Please refer to this link, it will give you a good idea about what to do especially in the south island.
Two weeks is a short time for New Zealand since it is such a diverse country. I'd recommend more two months so there is a danger of diluting your trip too much, trying to see to much & enjoying nothing. Perhaps you might consider doing one island or the other.
Many people prefer the south island because it has the dramatic southern Alps however I think the North Island has as much going for it but in a different way. Firstly you have the beautiful cities of Auckland & Wellington. There is the glow worm caves at Waitomo, similar can be seen in the south island, a boat trip from Queenstown. I found the north island better for getting to know the Maori culture and for volcanic activity. Rotorua is a major destination for the latter with its geysers, volcano, buried village etc. Lake Taupo is a caldera & one of the worlds 5 super volcanos. From there you can do the Tongariro Walk through volcanic scenery.
It also has a volcano musemn. There's even an off shore volcano at White Island off the Tauranga region.
The Bay of Islands up in the north has a great beach you can be driven along. From Pahia you can swim with dolphins as you can also do in the south island off Kaikoura if you book in advance enough. In Pahia you can go on every type of boat trip imaginable from tall ship sailing to a replica Maori canoe with 'Maori warriors' who will initiate you into some of their customs. Napier is the art deco town and scene of a very destructive earthquake decades back. The list is endless. almost 8 years ago