function popup(url,width,height,scrollbars)
  {
  	
  	if(width > 0 && height > 0)
  	{
  		var centered;
  		x = (screen.availWidth - width) / 2;
  		y = (screen.availHeight - height) / 2;
  		centered =',width=' + width + ',height=' + height + ',left=' + x + ',top=' + y + ',scrollbars='+scrollbars+',resizable=yes,status=yes';
  	}else
  	{
  		centered = 'scrollbars='+scrollbars+',resizable=yes,status=yes';
  	}	
  	var popup = window.open(url, '_blank', centered);
    	if (!popup.opener) popup.opener = self;
  	popup.focus();
  }