Intendi qualcosa del genere?
codice:
<html> 
<head> 
<script> 
function mostra(){
z=document.getElementById('TabHidden').style;
z.visibility=(z.visibility=='hidden')?'visible':'hidden';
}
</script>
<title></title> 
</head>
<body> 
<table border="0" width="10%">
 <tr>
    <td onClick="mostra()" style="cursor:hand">ciao</td>
 </tr>

 <tr>
  <table id="TabHidden" style="visibility:hidden" border="0">
  <tr>
    <td>ci</td>
    <td>ao</td>
  </tr>
  <tr>
    <td>ci</td>
    <td>ao</td>
  </tr>
  <tr>
    <td>ci</td>
    <td>ao</td>
  </tr>
  <tr>
    <td>ci</td>
    <td>ao</td>
  </tr>
  <tr>
    <td>ci</td>
    <td>ao</td>
  </tr>
 </tr>
</table>
</body>
</html>