You do NOT have to be in possession of a return ticket in order to obtain a Working Holiday Visa (which is what I assume you're referring to). The Australian Government's website actually states that you should not make any travel plans until AFTER you've obtained a visa. (The visa is then valid for entry into Australia for a period of 12 months and expires 12 months after the entry date. You may not work for the same employer for more than 6 months).
Start here:
http://www.immi.gov.a.../working-holiday/417/
Then click through the numbered links, at the bottom of each page, to get full information.
Chris