Look for family through National Archives and Military Service Records
I have found that I can search for my family through the Australia War Memorial website http://www.awm.gov.au
There are a variety of ways to use the site.
You may find that your family member was enlisted in the AIF- in the RAAF or RAN and there may be details of them on Nominal Rolls. These print outs show their age, their occupation, where they enlisted and what company they were assigned to.
There is a search part for Missing In Action that has been sorted by the Red Cross http://www.awm.gov.au/redcross/index.asp and AMF Prisoners of War and Missing in the Far East and South West Pacific Islands can be found on http://www.awm.gov.au/awm232/index.asp
The Roll of Honour at Canberra is replicated here. So if you know your family member died in the War then you should be able to find their detials here- http://www.awm.gov.au/roh/
Sometimes you can find out information like date of birth and old addresses from these military records.Birth records aren't as accessible as in previous times due to Privacy Laws.
There are a few other links so just surf around see what comes up with your surname.
The National Archives website is http://www.naa.gov.au/
You should join as a member as it is free. Go to Record Search at top of the first page. It will take you to where you log in and off you go
Here you will see Service Records of individuals, their service number and details where their records are kept.
If the records have been examined then they will have been scanned and available as digital copies for you to view, download and print off. If they haven't been examined then they haven't been scanned and not available yet. But it will tell you the Barcode and series number and if you wished you could go to the location and view on site I presume.
You only need to put in a Surname and not detail dates or conflicts. If you want to narrow your search then put in the full name as you know it.
I have found this a most enlightening and rewarding way to research those men and women that served our country in either World War One or Two. But for younger family members there is also a search area for Vietnam War, Korean etc.
I have even been able to obtain an Army photo of one of the men in my family. So that was wonderful.
Hope this helps some of you with your research.
Drop me a line if I can help you further.