function PopCenter(page, popW, popH) {
  var w = 480, h = 340;

  if (document.all || document.layers || screen.availWidth) {
     w = screen.availWidth;
     h = screen.availHeight;
  }

  if (!popW)
    popW = 450;
  if (!popH)
    popH = 350;

  var leftPos = (w-popW)/2, topPos = (h-popH)/2;

  window.open(page,'CourseDescription','width=' + popW + ',height=' + popH + ',top=' + topPos + ',left=' + leftPos + ',toolbar=no,location=no,scrollbars=yes,resizable=yes');
}