Hi Nel,
a study visa gives you a general permission to study, not to work.
Full-time students under a study permit are allowed to work during the week in order to compliment their study or during the holiday break. See below:

Working while studying
You can work part time while studying full time, under certain circumstances:

- to meet course requirements for practical work experience, or
- during the Christmas and New Year holiday period if you are in a full-time course of study lasting 12 months or longer, and/or
- for up to 20 hours in any given week during the academic year if you are in full-time study:
a) at a private training establishment or tertiary institution and taking at least two academic years to complete, or
b) culminating in a New Zealand qualification that would qualify for points under the Skilled Migrant Category, or
c) at a secondary school full year course of study in years 12 or 13, provided you have written permission from your school and written consent from your parent, or
d) in a full-time study course lasting at least six months, at a private training establishment or tertiary institution. Your visa or immigration officer has to be satisfied that the main purpose of your course of study is to develop English language skills, and, you have an International English Language Testing System (IELTS) overall band score of 5.0 or above (General or Academic Module), or
e) at a tertiary level of at least one academic year duration as part of an approved tertiary student exchange scheme.

If your course is 1 year long, you will be able to get in under the christmas period exception rule, just make sure that it is 12 months, rather than "one year" = academic year: February to December
Please refer to the NZ immigration website.
All about visas and permits

Good luck,
Andrea