Guarda questo esempio:
codice:
<script>
  function Switch(num) {
    if (num==1) {
      id1.style.display="block";
      id2.style.display="none";
    }
    else {
      id1.style.display="none";
      id2.style.display="block";
    }
  }
</script>

<body>
  <table border="1">
    <tr>
      <td onclick="Switch(1);">1</td>
      <td onclick="Switch(2);">2</td>
    </tr>
    <tr>
      <td colspan="2">
        <div id="id1">primo</div>
        <div id="id2" style="display:none;">secondo</div>
      </td>
    </tr>
  </table>
</body>