function popupwindow(url,name,w,h) {

LeftPosition = (screen.width) ? (screen.width- w)/2 : 0;
TopPosition = (screen.height) ? (screen.height- h)/2 : 0;

   var popup = window.open(url,name,"scrollbars=no,width="+w+",height="+h+",menubar=no,toolbar=no,top="+TopPosition+",left="+LeftPosition+",location=no,directories=no,resizable=no");

if (popup.focus) { popup.focus(); }
}