Australians cannot get a tax refund of the 30% withholding tax. The tax treaties between the USA and Australia doesn't permit it. Each country negotiates its own tax treaty and deals with gambling income differently.
At the IRS government site, they offer the forms for free. If you can't fill them out because they are too complicated, there are helpful sites that to visit. See the Related Links below for the IRS site and others.
For a list of qualifying countries please see the related links.