To make the flat rate shipping for these selections you would need to first capture the selected country that the user chooses and store the value in a session variable. Next you would craft your shipping charge rules and based on the value held in this session variable you would use one rate versus another.
To capture the country in a session variable add a set session value server behavior to your page. For the trigger use the bindings and select the checkout form element for the country. For the value you will choose the same element.
Once you have done this you can create the rule. In your charge rules you will first check to see if the session variable that holds the value for the country exists, if it does then the next condition in the trigger will be to see if it equals your first country value. If it does then you would apply the flat rate for that country in the calculation portion.
You would repeat this for each of the countries making sure to apply the correct flate rate amount for each. Please post back with any additional questions that you have about any part of this.
