Untitled

<html>
  <head>
    <title>Main window</title>
    <script type="text/javascript">
      var popupwindow = '';

      function popupSelectItem(url) {
        if (!popupwindow.closed && popupwindow.location) {
          popupwindow.location.href = url;
        }
        else {
          popupwindow=window.open(url, 'name', 'height=200,width=150');
          if (!popupwindow.opener) {
            popupwindow.opener = self;
          }
        }
        if (window.focus) {
          popupwindow.focus();
        }
        return false;
      }
    </script>
  </head>
  <body>
    <form>
      Selected item:
      <input id="selectedItem" type="text">
      <input type="button" value="Choose an item" onclick="popupSelectItem('popup.html')">
    </form>
  </body>
</html>