var popup_window = null;
    
function popup(status, url, width, height, x, y) {
 var a = width;
 var b = height;
 var winStats;

 if (navigator.appName.indexOf("Microsoft")>=0) {
  winStats +=",left=";
  winStats += x;
  winStats += ",top=";
  winStats += y;
 }

 if(status != 0) {
  if(popup != null) popup.focus(); 
  else { 
   var popup = open(url,'Popup', 'location=no,scrollbars=yes,toolbar=no,directories=no,menubar=no,titlebar=no,personalbar=no,width='+a+',height='+b + winStats);
   popup_window = popup;
  }
 } else {
 if(popup_window != null) popup_window.close();
 }
 popup.focus();
}