http://www.snopes.com/crime/statistics/ausguns.asp

The main point to be learned here is that determining the effect of changes in Australia's gun ownership laws and the government's firearm buy-back program on crime rates requires a complex long-term analysis and can't be discerned from the small, mixed grab bag of short-term statistics offered here. And no matter what the outcome of that analysis, the results aren't necessarily applicable to the USA, where laws regarding gun ownership are (and always have been) much different than those in Australia.