Hey Karl,
I am currently in NZ with my husband. We are from the UK and have been here for nearly 8 months. Fruit picking is readily available if your willing, as is working in the fruit packing biz. We did a stint in a blueberry packing place, and we are now working in the Lake Taupo area. I am doing some child minding, and the husband is working as a waiter. We came over on a Working Holiday Visa, and thought that it would be quite easy to get a temp job in the city (in our case Auckland). We both come from office jobs (banking and civil service), but we could not get a job for love nor money! I guess with the economic climate being as it is, and the type of visa we have just wasn't what people were looking for. Plus, lots of companies advertise temporary jobs, but when you apply they turn out to be "ongoing" etc.
I would advise on applying for a work visa before arriving. It can be done online and costs about $120 NZ for a Working Holiday visa. The turn around for these applications is pretty swift with ours taking just 48 hours to be approved. Go to http://www.immigration.govt.nz/migrant/stream/work/workingholiday/ for info and to apply.
Getting a bank account is easy and just takes a few days. We signed up for an account with Kiwibank (through the postshop) which is free to use and provides you with an EFTPOS card for transactions. We did it all at the Postshop on Customs Street in Auckland and had the cards sent there. You need your passport, a letter from your hostel with their address on it, and a small amount of money to open the account with. They even sort out internet banking there and then if you want that. It takes a few days for your bank card to arrive, but you can choose to have a non-personalised card (without your name on), which you can have there and then if you don't plan on hanging around too long. Getting an IRD number is easy too. You fill in the form, take it to the Postshop where they copy and validate your documents (passport, drivers licence etc), and then they send it off for you. You can go to http://www.ird.govt.nz/how-to/irdnumbers/ for more info.
There are lots of jobs available when summer comes around from working as a waiter to fruit picking, working for Greenpeace or cleaning hostels. You can sign up with Hays Global Link before you arrive in the country, and they can help you obtain work from the outset.
Good websites for job searching are:
http://www.gapyear-newzealand.co.uk/work/index.php
http://www.seasonalwork.co.nz
http://www.seek.co.nz
http://www.providore.co.nz
http://www.hukapak.co.nz/
https://www.satara.co.nz/seasonalwork/
http://www.workinnz.co.nz/job_details/
http://www.0800labour.co.nz/
http://www.hairyberrynz.com/
http://www.hitnz.co.nz
http://www.picknz.co.nz/
http://www.seasonaljobs.co.nz
http://www.backpackerboard.co.nz/
http://www.trademe.co.nz (also good for finding a campervan to buy or somewhere to rent temporarily)
Auckland is a good place to start, and has plenty of places to stay right in the heart of the city. We stayed at City Lodge accomodation on Vincent Street, just 10 minutes walk fromn Queen Street, or a cheap 50c bus trip down to the Britomart. We had a double, ensuite, which was $65 a night. The YHA is on the same street.
Please feel free to contact me if you have any questions. I have plenty of answers!!