I assume that you mean that the payment page is showing as UK information when you try to subscribe.
Do the following:
Open Internet Explorer and go to Tools/Internet Options.
On the General tab click the Languages button.
If the language shown is English-UK and you are in another country where OneCare is available for sale, change the language to that country by selecting Add, finding the language country combination in the list for English-Australia, in your case, and selecting it. Once it has been added, remove English-UK from the list using the remove button.
See if that resolves it for you.
-steve