There are a few that are having trouble getting this to work so i have made it that easy that it should work for everyone, basically there are 2 downloads that you require.
NavnGo8.rar which contains all the required files
NavnGo_Australia8_R14_071017.rar which is the Australia Map for NavnGo
Download these two rar files and once you get them both, unrar them to your hard disk in a folder of your choice, once there unrared you should have these folders
and also the Australia8_R14_071017 map on its own
move the map into the following folder iGO8\content\map
Get your SD card and put it in your card reader or whatever you use and copy these two folders over to the ROOT folder on your SD card.
Put SD card back in your PDA and it should automatically start up and ask you to install the program, just follow instructions for installation.