You need to become an Incorporated Association.
Find out about them here:
http://www.fairtrading.nsw.gov.au/bu...ociations.html
Download a constitution (which you can change/amend) here:
http://www.fairtrading.nsw.gov.au/pd...ons/dft119.pdf
The first page tells you all about starting one up, how to, and the benefits, aswell as running an association.
Hix