function centra(url, width, height)
   {
   if (document.all)
      {
      var x = window.screenLeft;
      var y = window.screenTop;
      var w = window.document.body.offsetWidth;
      var h = window.document.body.offsetHeight;
	  var cntx = x + Math.round((w - width) / 2);
      var cnty = y + Math.round((h - height) / 2);
	  window.open (url, null, 'left=' + cntx + ',top=' + cnty + ',width=' + width + ',height=' + height);
//	  window.showModelessDialog (url,"",'help:0;left:'+cntx+';top:'+cnty+';resizable:1;dialogWidth='+width+';dialogHeight='+height);
      }
  else
   {
   var x = window.screenX;
   var y = window.screenY;
   var w = window.outerWidth;
   var h = window.outerHeight;
   var cntx = x + Math.round((w - width) / 2);
   var cnty = y + Math.round((h - height) / 2);
   window.open (url, null, 'left=' + cntx + ',top=' + cnty + ',width=' + width + ',height=' + height);
   }

}