If you don't already have a GPS I'd just pick one up in Perth. I've used a few free maps in several countries and they're quite helpful for presenting a moving map, but are limited in other functions. Just suggested it as a budget friendly option especially if you're not going to be there long.

I'm in Oz a lot & picked up a cheapie Garmin at Officeworks a few years back. In addition to the turn-by-turn voice navigation the database knows the speed limits on most used streets and highways and will chime when you go over. This can be a lifesaver as many speed limits in Oz seem quite slow compared to the US and they're much more stringent in enforcement (/me looks YOUR way Victoria.) Many times I'll see a 45 kph limit on a road that feels like it should be 50 mph. The database also knows about speed/red light cameras and like ROW2Aisle points out the POIs are much better.

On a side note - in the States I have my Garmin set to use the Aussie voice 'Karen' for navigation (um, shouldn't it be 'Kazza'?) and it's a hoot driving around Southern California with all the spanish street names.