Three ways that I'm aware of for "free" membership.
1. Sign up for an Earth or Earth+ card from Westpac (
http://www.earth.com.au). Free membership to the Qantas FF scheme comes with the card and there is no annual fee for the first year. (Although, the free FF membership is for a limited time. Don't know when that will end)
2. Join the Qantas club. (Costs $ of course). You get "free" membership then.
3. If you live overseas (aka have a mailing address overseas apart from NZ) you can join for free. A little bit of a dodgy method and may not be advisable. Eventually you'll move back to Australia.