hard to give you advice when you havent said what time of year they want to travel , but for starters I would look at SQ
often have good fares as well , but be aware that all their flights to New Zealand transit Australia and some nationalities require transit visas even for same aircraft transit through Australia . If they have never travelled long haul before then I would recommend that they consider breaking the journey in each direction , even just for one night - often cheap deals can be found in SIN
edited to add :
PS both SQ and EK fly into both AKL and CHC .
If they want to travel around New Zealand sightseeing an open jaw itinerary can avoid the need to waste time and money getting back to original point of entry . Dont be fooled by the fact that on a map New Zealand looks tiny compared to its giant neighbour , it is a long thin country .
[Edited 2009-07-20 01:28:10]