function popup() {
  var wndHeight = 516;
  var wndWidth = 633;
  var X = 0;
  var Y = 0;
  if (screen.availWidth){
    X = (screen.availWidth / 2) - (wndWidth / 2);
    Y = (screen.availHeight / 2) - (wndHeight / 2);
  }

  window.open("popup/pop.htm","m101","left=" + X + "screenX=" + X + "screenY=" + Y + ",top=" + Y + ",toolbar=0,scrollbars=1,resizable=0,height=516,width=633");
}