If you're not paying any tax in the country that you're earning the money then the ATO will expect you to pay the same amount of tax as if you earned all the money here in Australia (ie, put money aside for your tax bill at the end of the year).
If you pay tax in the country where you are earning the money then you should get a statement from your employer stating how much tax you have paid overseas. The ATO will expect you to pay the difference that you would have normally paid in Australia to what you have paid overseas. (I'm currently in this boat flying in the Solomon islands - equal time FIFO).
The 183 day rule no longer exists (thanks Rudd and Labour). You either have to move out of Australia all together and reside somewhere else (no longer be a resident of Australia for tax purposes), but if you are coming back to Australia that will be difficult to prove.
If you are earning money in a tax free country the ATO will come after you for their chunk of change.
There's not many scenarios where you can earn tax free money overseas these days, one example is if you're working as part of a recognised force (eg contractor in afghanistan or timor etc) and not have to give the ATO a cent.
Speak to an accountant, but the days of working for more than 183 days out of the country and banking the whole amount are long gone.
Last edited by havick; 5th June 2012 at 21:31.