Special tax rules apply for those who enter Australia on a temporary visa, an example of which would be the 457 visa. It is good news, to encourage you to come!
Whilst you are a temporary resident for tax purposes you only need to declare and pay tax on Australian derived income. This means, for example, that there is no tax on any rental income earned from your overseas property, and no capital gains tax on the sale of non-Australian assets.
So when, I hear you ask, does this utopian phase expire? The answer is the minute you apply for permanent residency, or the minute you shack up with an Australian citizen. So don’t fall in love with an Ozzie – socialise only with other expats just to be on the safe side!
More information is available here.