G'day Jodie,
You need FSX and over 1GB of disk space free wherever you have FSX installed.
Head on over to FTX.
The first item is Called AU Blue. This is a free download that updates all the textures, roads, scenery for Tasmania. I imaging it includes their normal install guide i the package, it contains lots of info about FSX settings to get the best out of your machine.
the second item on the page is a set of freeware airports. They are all small airfields and bush strips. Aldinga is in there. You must download version 2.0, 2.1 and 2.2 and install them in that order.
The third item on the page gives you a better representation of hills and mountains.
None of these installs make the FSX performance worse and in many cases the installation of the ORBX scenery actually improves performance.
Steven.