Where are you from? What passport do you have? Without these details impossible to say for sure.
Check out: http://www.immi.gov.au/visawizard/
You may or may not need a visa depending on your country of origin.
Normally a return or onward flight is required for entry, unless you are from New Zealand. over 9 years ago
If you are staying for less than 3 months its unlikely you'll need a visa (depending on where you're from) but to be sure check on http://www.anyworkanywhere.lnk.visafirst.com/
As for flights/transportation, if you're doing it on the cheap I would suggest flying on jetstar, virgin blue or tiger airways (tiger is the cheapest but not quite as comfortable).
Or if you're traveling A LOT I'd advise buying a $250 rail pass for unlimited travel to 360 destinations for the whole month. http://www.railaustralia.com.au/backtracker.php
Good luck, and have fun! over 9 years ago