Hi there, Recently I found out about a wonderful invention called Warka Water. It was designed to bring potable water to arid Ethiopian communities. It works by collecting moisture straight out of the air and harvesting it as dew, then collecting it for use. The design is open source so anyone can have access to it, so there actually is a way to go about greening Australia's interior which is quite affordable. If anyone else would like to actually embark on a feasibility study for the project, I'd be delighted to lend a hand. Here's a link to a little video which explains the device:
There's are simpler low tech ways to collect water in the desert. Building swales is the most obvious. As are pit plantings. You can also make piles of stones and plant your trees on the other side of the pile. That will create condensation at night and underneath the pile of stones will usually remain moist if the pile is big enough.