If it's this model: http://www.samsung.com/au/consumer/tv-audio-video/television/archive/PS43D450A2MXXY-spec
Then it doesn't show networking as a feature, and a firmware upgrade or a wireless adapter isn't going to help, as the TV needs some additional pieces of internal hardware in order to get a network connection.
Now admittedly, I support US products and customers, so I might have missed a finer point your Australian model. So if you want Samsung help from your country, here's the Samsung Australian portal for support on that product: http://www.samsung.com/au/support/model/PS43D450A2MXXY
I have a samsung PS43D450 and i have bought as wireless usb WIS12ABGNX when plugged in the TV doesnt recognise any thing has been plugged in.
It does recognise a USB pen drive.
When I go to the menu section I cannot see any menu titled NETWORK.
Just updated to latest firmware but getting no joy any help would be appreciated