|Hi Chloe, have you tried using google to research for a laptop internal modem card or possibly an external usb modem?|
Make sure both the modem and the software (application, not driver) that comes with it supports a NZ pstn connection, and the internet.
I do not know NZ conditions, but here in the UK a broadband and telephone connection including free national and international calls to many countries 24/7 can be found for around £20 or less a month. This includes a wireless router so all the family can surf at the same time.
This is cheaper than having just a telephone line service from British Telecom.
Broadband is vastly superior than dial up.
Good Luck - Keep us posted.