function popupcenter(url,wwidth,wheight) {
 var wleft = (screen.width - wwidth) / 2;
 var wtop = (screen.height - wheight) / 2;
 params  = 'width='+wwidth;
 params += ', height='+wheight;
 params += ', top='+wtop;
 params += ', left='+wleft;
 params += ', toolbar=no,location=no,scrollbars=yes,resizable=yes';
 newwin=window.open(url,'windowcalled', params);
 if (window.focus) {newwin.focus()}
 return false;
}