I've been playing with maps downloaded from Geoscience Australia: MapConnect (.ecw files) OziExplorer has no problems using these maps and I've got them up and running on a Mio Moov A430 (I'd suggest buying a gps that has a SD card slot - it makes all the installation much easier.).
Its a free service and the maps are issued under the creative common's licensing.
The main downside is that it doesn't have all the aviation overlays (can show airstrips etc). I'm not overly concerned about that as we have to carry the paper charts anyway.
The other downside is the scale is 1:250 000, as opposed to the 1:500 000 the VNC charts are. Not really a huge problem, as if you can use im2ozf to convert the images to the OziExplorer image format and zoom out 50% at the same time.
I can provide my session file (has a bunch of overlay options I think might be useful turned on) if anybody wants to save themselves a couple of minutes. The maps are probably a tad on the busy side, but certainly usable.
I've also .ecw files downloaded for most of sth eastern nsw and eastern victoria (basically sydney to just north of melbourne, plus inland a fair way), which I'm happy to upload somewhere if people are interested.