Quote Originally Posted by royaldave View Post
No, must admit not sure how to do that. That said I am more interested in your prior comment -

That hidden input is most likely being "overwritten" by the base form's address-selection

To this person who is pretty rubbish at forms, what does this mean, and where would I look to correct this ?
You need to "View Source" when the checkout_one page is presented (that's Ctrl+U on FireFox) to see if there are multiple inputs named zone_country_id[ship].

Setting up an AU Zone for shipping is fairly simple (although multi-step):

Localizations->Zone Definitions, click Insert. Zone Name: AU Shipping Zone Description: Limit shipping to AU-only, press Enter.
Now, click the Details button associated with that Zone Definition: Country: AU Zone: All Zones (some versions of Zen Cart show this as Please select), press Enter.

Now navigate to Modules->Shipping. Select each of your active shipping modules and set the Shipping Zone to AU Shipping. That will enable those shipping selections to be active only when the ship-to address is in Australia.