$ship_to = JRequest::getVar('ship_to_info_id');

if ($ship_to != '') {

  $my_id = $db->Quote( $db->getEscaped( $ship_to ) );

  $sql = "select country from #__vm_user_info where user_info_id = $my_id";

  $db->setQuery( $sql, 0, 1 ); 

  $row = $db->loadObject(); 

  $country = @$row->country;

  if ($country == 'USA') return XXX; /* replace XXX with the module id to use for USA shipping addresses. */

}