Sim is correct. It is only available to those who actually paid tax last year, no matter how small an amount it is.
I was talking to my accountant about it the other day and he was telling me that it is amazing the people that this package has brought out of the woodwork, hoping to get a payment. He said that there are quite a few people who have not lodged a return, some for several years, but they have all now done it, so they can get the stimulous. Some of these with very negative results for them, not the ATO.
There are a lot of people that believe that if they lodge a return they will automatically get it. He cited one case, where an individual had not lodged a return for over 5 years and had a tax liability of over $55k which had not been paid. He's just done his back taxes so he can claim the $900.