Re: Message on checkout when country selected
Since this is for the OPC if you add it to the template file only it will trigger the message show/not on page load only. It will not work when country is selected from the dropdown or address book (depends on the template though). OPC has a lot of js code to refresh different parts of the page on request.
The country dropdown triggers onChange event to properly display states field - this is where you want to add your message too to either pop or show directly on page. I think the file to modify is skin/common_files/js/change_states.js
You also have to modify skin/common_files/modules/One_Page_Checkout/ajax.checkout.js to show/hide the message if address is selected from the address book