Residents of any country can apply for a six month work visa for New Zealand if you need to complete a work placement as part of your University Degree. This visa can also be extended for a further six months if both the placement student and employer agree. This is a general work visa and you would be applying under the 'Student and Trainee' Policy.
You must be apply to supply the following for this visa:
support from your college or University
proof that you are enrolled on a course that requires a work placement
x-ray certificate (depending on your country of residence)
To obtain a visa you need to complete the Application to work in New Zealand form (NZIS 1015) and then send this along with the evidence above to your local NZ Immigration office. Employers generally offer Internships in areas such as Hospitality, Forestry or Tourism although persistence could find you other job offers!