The North island's geography is very different than the South Island.  The terrain on the north island is much more flat.

In order to get to Queenstown, we needed to drive from Auckland to Wellington and then catch the ferry from Wellington (North Island)

to Picton (South Island).  There is one set of ranges:

It's about an 8 hour drive to Wellington from Auckland.  While the distance makes you think 8 hours is way too long, the reality

is that New Zealand roads are for the most part 2 lanes and very curvy.  Once you get to Wellington, you can take the ferry across.

It's a passenger and vehicle ferry.

The journey across the Cook straits is about 3 hours. The actual straits is not that long and you can sometimes see the other ferry

as it comes back across.

There are two types of ferry services, high speed and regular.  If you go during the summer you can get the high speed ferry.  You definitely

want to get sea sickness pills.  It takes about 25 minutes to get out of the Wellington Harbor and the about 45min to hour in the straits.

The largest portion of time is spent in the channels of the South Island as you work your way to Picton. 

Here is a Video clip of the Ferry Ride: Its about 3.5 Megs.