das,
We were there a few months ago and brought back 2 cases as checked baggage. We were travelling on CX and had no problems. You shouldn't have a problem on any airline as long as you pay attention to their baggage policies. Note that the baggage rules to/from the US are more liberal than to other destinations from NZ. We're going back next year and will only take 1 suitcase so we can bring back 3 cases as baggage. This was the first time we had brought back wine from an international destination, but we have checked cases of wine as luggage on domestic flights on several occasions without problem (as long as they are properly packaged).
Once you get to AKL, check the yellow pages in the phone book for a air freight company by the name of TNT. They will sell you 12 bottle wine shippers for about $10US each. They will also ship the wine for about $85US per case, which is too high for me, but cheaper than some AKL wine stores (especally in the downtown area).
Personally, I felt like I was committing robbery at times buying NZ wine with $US. You can buy some very nice stuff for $12-15US. Just last night, we had a great Coopers Creek Swamp Reserve Chard that we bought for about $13US. When we were there last time we only visited the North Island and didn't make it to Marlborough (on our itinerary for next year). However, we were suprised at the quality of the non-SB varietals. The Chards were surprisingly nice and the top Merlots were as good as most in the US. Additionally, they are making some interesting Syrahs in the Rhone style (and some similar to the Australian shirazs). Other interesting reds include Bourdeaux style blends with a predominance of Merlot rather than CabS and Rhone style blends.
If you have any questions, just ask. Note that most of the wineries on Waiheke Island (near AKL) are small and only open during the local summer.