The currency in New Zealand is the New Zealand Dollar (NZD).  It is easily exchangable with all other major currencies and it is accepted throughout the country.  

100 cents = 1 Dollar
coins: 10 cents, 20 cents, 50 cents, 1 dollar, 2 dollars
notes: 5 dollars, 10 dollars, 20 dollars, 50 dollars, 100 dollars



By way of information, you certainly have an opportunity to save yourself money on currency exchanges using the many available ATM machines.  Most currency exchanges give fairly unfavorable rates and then add a fee or commission to the transaction (you will usually see them "buying" currency for 3-6% less than it is worth and "selling" you NZ Dollars for 3-6% more than they are worth, then adding a fee of $2-10).  For those who use, say Bank of America, you can use WestPac Bank ATMs with no ATM fees or charges and a fair exchange rate (with no fees or commissions).  There are also a fair amount of Citi ATMs there and in Australia.  Two other benefits: you will be traveling with less cash and you can take out only the amount of money you actually need - preventing you from being stuck holding a bunch of NZ Dollars or getting a poor exchange back at the end of your trip.