function popup(popupUrl, popupName, height, width) {
  var winFeatures = "height=" + height + ",innerHeight=" + height;
  winFeatures += ",width=" + width + ",innerWidth=" + width;  
  if (window.screen) {
    var ah = screen.availHeight - 30;
    var aw = screen.availWidth - 10;
    var xc = (aw - width) / 2;
    var yc = (ah - height) / 2;
    winFeatures += ",left=" + xc + ",screenX=" + xc;
    winFeatures += ",top=" + yc + ",screenY=" + yc;
    winFeatures += ",resizable,scrollbars";
  }
  sampleWindow = window.open(popupUrl, popupName, winFeatures);
  sampleWindow.focus();
  return false;
}