To answer your question about DEM's for Australia, probably not likely, not in anything useable anyway. International DEM data has always been really hard to come by to begin with, and the only global data I've seen is only detailed enough to show that "yes, theres a range of mountains in this location" and I believe are 90 meter resolution (as opposed to 10 meter resolution for the U.S. and 3 meter resolution for some small parts of U.S. You might try doing a search for "global DEM data" or something to that effect, I can't remember where I found it as it was a few years back.