Popup-Fenster zentrieren

[herbalizer]

<script type="text/javascript">
  <!--
  sw = (screen.width-680)/2;
  sh = (screen.height-415)/2;
  window.open('start.html','main','width=680,height=415,left=sw,top=sh,location=no,menubar=no,resizable=no,scrollbars=no,status=no,toolbar=no');
  //-->
</script>

Das 3. Argument in window.open() ist ein String. Also machst du folgendes:
<script type="text/javascript">
   <!--
   sw = (screen.width-680)/2;
   sh = (screen.height-415)/2;
   geom = 'width=680,height=415,left='+sw+',top='+sh+',location=no,menubar=no,resizable=no,scrollbars=no,status=no,toolbar=no'
   window.open('start.html','main',geom);
   //-->
</script>