/**
  * creates a popup
  *
	* @param string s_url url to open within the popup
  * @param integer n_width width of the popup
  * @param integer n_height height of the popup
  * @param string s_params additional parameters for the popup
	* @return void
  */
  function open_popup(s_url, n_width, n_height, s_params) {
    var s_win_param = 'width=' + n_width + ',height=' + n_height;
    if (s_params != '') {
      s_win_param += ',' + s_params;
      // scrollbars=yes,resizable=1,menubar=no
    } // end: if
    
    popup = window.open(s_url, 'popup', s_win_param);
    popup.focus();
  } // end: function open_popup()