function centerPop(url, winWidth, winHeight) {
  var screenPosX,screenPosY;
  screenPosX = (screen.availWidth - winWidth) / 2;
  screenPosY = (screen.availHeight - winHeight) / 2 - 100;
  newwin = window.open(url, 'subwin','toolbar=0,location=0,directories=0,status=0,menubar=0,scrollbars=1,resizable=1, copyhistory=0,width='+winWidth+',height='+winHeight+',screenX='+screenPosX+',screenY='+screenPosY+',left='+screenPosX+',top='+screenPosY+'');
  newwin.resizeTo(winWidth, winHeight);
  newwin.focus();
}