Where & how do I download the geo Natmaps

I have gone around & around on the Natmap website trying to find what I need to download to get the desired basic Geo files for use on OziExplorer.  I have access to a couple of samples for West Pilbara (Yanrey SF50-9), provided by others, but need the base maps for other goldfield sites (all states really).  

So has anyone got a step by step answer to accessing the required data.

Thanks,

Here you go Pablop;

http://www.ga.gov.au/scientific-topics/geographic-information/topographic-maps-data/digital-topographic-maps/product-troubleshooting/natmap-2005-2008

Thanks for the link Nightjar, I had been in here before and I was really no wiser.  But at the following address I have been able to find a map of Oz where you can select what you want to download.  Is this what you have used?

http://www.geoscience.gov.au/cgi-bin/mapserv?map=/nas/web/ops/prod/apps_www-d/mapserver/geoportal-geologicalmaps/index.map&mode=browse&layer=map250&queryon=true

I hope that this is what I need, so will play with it for a while and see what comes out in the wash.

After a lot of messing around I was able to download Geological maps for specific areas, but I am not sure if these are the best ones to use as there is basically only a couple of very main roads and the geology info is very in your face.

Perhaps I need to find an alternative, what do others use?