var oWin;
function show(sSrc) {
  if (!oWin|| oWin.closed || oWin.document.location != sSrc) {
    var iWidth = 640;
    var iHeight = 480;
    var i_y = parseInt((screen.availHeight - iHeight) / 2, 10);
    var i_x = parseInt((screen.availWidth - iWidth) / 2, 10);
    oWin = window.open(sSrc, "newWindow", "height=" + iHeight + ", width= " + iWidth + ",left=" + i_x + ", top=" + i_y + ", toolbar=0, menubar=0, scrollbars=no, resizable=no");
    oWin.focus();
    } else {
    // bring existing subwindow to the front
      oWin.focus();
    }
}