In brief, The First Home Owners Grant has been given a boost as follows:
First home buyers who purchase established homes will now receive a grant of $14,000
First home buyers who contract to build a new home or purchase a spec type, newly constructed home will receive a grant of $21,000.
To qualify for a grant you must have never owned or had an interest in a residential property other than a block of vacant land. The same seems to apply if your spouse/domestic partner previously owned a residential property anywhere in Australia. According to the SA government fact sheet, a spouse/domestic partner must be included on your application.
The boost is applicable to contracts signed between October 14 2008 and June 30 2009.
For clarification of your position I suggest you contact a reputable mortgage broker, they will also be able to advise you about which lenders can be used to take advantage of the grant. You may also want to consult the relevant Government Department in your state. I also suggest you get information on the First Home Buyers Deposit Saver Scheme as well.
Property developers and vacant land owners should benefit from these changes the most. So if you have a piece of land that has development potential, get moving. This is why I like investment properties on their own title. The opportunities for wealth creation are always there, even in tough economic times.