$previous_database = db_set_active('seperate_db')
db_set_active($previous_database);

function swap_db_form_alter($form_id, &$form) {

  // Send profile data to external database.

  if (isset($form['type']) && 'edit-profile' == $form_id) {
    if (db_result(db_query("SELECT fid FROM {profile_fields} WHERE username = '%s'". $query_suffix, $args2))) {
      

     // Table Insert Stuff

    }
  }
}

db_set_active();