You can read more about xhtml table markup in HTML Dog’s Table Section. I have tested the tables below in Mozilla Firefox 3, IE 6 and 7, Opera 9.x and Safari.
<!-- Table markup-->
<table id="...">
<!-- Table header -->
<thead>
<tr>
<th scope="col" id="...">...</th>
...
</tr>
</thead>
<!-- Table footer -->
<tfoot>
<tr>
<td>...</td>
</tr>
</tfoot>
<!-- Table body -->
<tbody>
<tr>
<td>...</td>
...
</tr>
...
</tbody>
</table>