var vent=0
function popup(que,wid,hei,scrollbars,windowName) {
if (vent && navigator.appName=='Microsoft Internet Explorer') vent.close();
 Izda=(screen.width-wid)/2
 Arriba=(screen.height-hei)/2
 cadena='width='+wid+',height='+hei+',top='+Arriba+',left='+Izda+',toolbar=no,location=no,status=no,menubar=no,resizable=yes,scrollbars=' + scrollbars
 if (windowName==""){
 	windowName='windowName'
 }
 vent=window.open(que,windowName,cadena)
 vent.focus()
 }