Hi Chris,
Sorry to disappoint but it won't be visible from Australia because the Moon won't be above the local horizon at the time. The Moon will rise about 2 hrs after impact and it'll be all well and truly over by the time it's up.
You can watch it all on NASA TV here:
http://www.nasa.gov/mission_pages/LC...ain/index.html
However, web traffic will be high and it might be hard to get on and stay on.
If the Moon were above the horizon at the time of impact, many have said the debris plume excavated by the impact would probably be visible in a 10" (25cm) 'scope.
Best,
Les D