It is very easy to build a Google Gadget with GWT. Here are the magic lines :

<?xml version="1.0" encoding="UTF-8"?>
<Module>
  <ModulePrefs title="Keyboard Warrior" description="Challenge your friends to a typing speed and accuracy match.">
  </ModulePrefs>
  <Content type="html">
    <![CDATA[
  <html>
    <head>
      <title>Keyboard Warrior</title>
    </head>
  
   <body>
      <script src="http://www.........com/ongwt.ikw.IKeyboardWarrior-xs.nocache.js"></script>
   </body>
  </html>
      ]]>
  </Content>
</Module>


You can try this GWT gadget : Add to Google