After lasts nights wonderful talk by Ellen, I have got together my collection of links that just might help you find what your ancestor did in WW1.
http://www.aif.adfa.edu.au:8080/index.html This is the AIF Data base.
http://www.awm.gov.au/ The Australian War Memorial.
http://trove.nla.gov.au/ Trove, for newspapers.
http://www.naa.gov.au/ National Archives, Australia.
http://mappingouranzacs.naa.gov.au/ A new site Mapping our ANZACS.
http://discoveringanzacs.naa.gov.au/home/ Another new site, Discovering ANZACS.
www.forces-war-records.co.uk/ww2-records These two are UK records.
Hope they help.