If you follow the letter of the law, you must have a firearm licence of the appropriate category to own an airsoft weapon, and it must have a unique serial number etc - its treated in the same way a shotgun or non-semi-automatic rifle is treated, which is harsh...

This is a good page on gun politics in Australia - [link=http://en.wikipedia.org/wiki/Gun_politics_in_Australia]LINK[/link]