Curcuma zedoaria would probably be okay for you as it is dormant in winter appearing again in the spring. As Sth Australia can have wet winters you may be better keeping it as a potted specimen so that the rhizomes do not rot away in wet cold soil. The occasional rainy day is okay.
Curcumas were the feature plant in the January edition of Tropical Topics which is the journal of The International Tropical Foliage & Garden Society inc.

Thanks tamoure, I am actually growing a few tropical gingers in pots down here already. Curcuma domestica and Kaempferia rotunda. They are doing really well for me but I had Kaempferia galanga and Boesenbergia rotunda a.k.a. pandurata but they did exactly what you said, grew well the first summer and then rotted in the pots over winter. I was devistated. I kept hoping and hoping that they would sprout but they never did and eventually I dug them up out of despiration and found the tubers hollow and rotted. :(

Hi jamus, try the ginger page on U.S. gardenweb (if you havn't already). It's got a lot of good ideas for wintering your rhizomes.
I bought my first gingers last summer. Being in north queensland I left the rhizomes in pots in the garden and only lost just one.
Since sprouting 2-3 months ago they have been vigourous enough to need repotting twice, and today planted in the garden!
I have also found that decorative pots generally don't have enough drainage for them.
on another subject, where are you in S.A.? We have family in the riverland.
Ree

Hi ree ree, thanks for the tips. I'm going to get the masonary drill out and put some more drainage holes in the pots. My Turmeric is LOVING the hot weather we're having. It's grown huge, half a metre tall and so lush. I'm in the Adelaide hills near Blackwood. Where abouts in the riverland are your family?