There are numerous ways to get turn by turn navigation on your PDA.
The easiest and legal way of doing it is to head to http://www.tomtom.com
Download the software. Then head over to "Buy now" and select "NAVIGATOR 6" as your product then select "Map of Australia". Continue through the checkout. It will cost you around $150 for the mapping but its well worth it. Also you'll need some kind of GPS, a bluetooth gps is easily the best option if your PDA does not have one built in. These can be found on ebay for less then $80AUD.
ok thats the lazymans option.

Other options mean getting the software and maps from a mate or another source *wink wink* and loading them up yourself.
Im not going to write on here how to do it as that would be illegal.

However im sure there is someone on here that would know and probably willing to help you out.

UPDATE: This is the link to the navigator software on the tomtom.com site. However its no longer available, best bet would be to google it or buy it from your local GPS dealer.
http://www.tomtom.com/products/product. ... ry=2&Lid=1
failing this let CC Communications know you want it and i'll source you a copy and a price.