What you will need is called a "Special Pilot Licence" It lets you use your existing licence provided that it and your medical are current. Once you have one, you should really only need a check flight (and obviously a briefing on local rules and procedures) from the company you hire from.
The other option is to covert your licence to an Australian licence. I wouldn't recommend this if you're only here for a little while as it requires a full PPL flight test and an Air Law theory exam.
Have a look at the CASA website - it contains the relevant forms
http://casa.gov.au/fcl/overbr.htm#special
I would recomment you allow 3-4 months to obtain the Special Pilot Licence (CASA say 8 weeks for processing but that could be a bit optimistic for an overseas application).
Aus is a great place to fly. It might be a bit of a hassle to sort out the paperwork but well worth it.
[Note: If you apply for one of these, when filling out form 639, make sure it is complete or they will send it back. Also include proper passport quality photos and make sure your signature is completely within the box. You will need to apply for either an ASIC or AVID (security check) I recommend an ASIC as it allows you to land pretty much anywhere.]