The Mixed Member Proportional or MMP system is used to elect representatives, so you have a vote both for a political party and a local representative. Although (as in the UK) there are two main political parties, the MMP system tends to result in some interesting coalition governments involving minority parties.
Once you are a permanent resident in New Zealand and have lived here for one year, and provided you are 18 years of age, you are required by law to register to vote. Your details are held on the Parliamentary Electoral Roll, and you need to keep your details updated when you move house. You are not however legally required to vote. For more information on registering to vote, voting and elections, see elections.org.nz.
For basic information on the political system in New Zealand, please see the parliament website. For more detailed information, try the Government Web Portal. This article was contributed by Jeremy Henderson from Broadbase International. Their UK website, www.broadbaseimmigration.co.uk, has a great range of up-to-date articles on life in New Zealand written especially for prospective migrants.