you would need a table to hold the countries and zones:
shippingzoneID - Primary Key
shippingzoneCountry - Country Abbreviation (IE, UK, DE, US, etc...)
shippingzoneZone - Zone (1,2,3,4)
the selected shipping country will be stored in a session variable named "eCartCheckoutForm_shipping_Country"
create a recordset that filters the shippingzoneCountry column on the eCartCheckoutForm_shipping_Country to return the correct zone, store that in another session.
Create a rule for each zone, and use the session variable holding the zone as the trigger.