html table multiple header rows
This is how I would do it (working fiddle at http://jsfiddle.net/7pDqb/) Tested in Chrome.
th, td { border: 1px solid black }
<table>
<thead>
<tr>
<th colspan="2">Major 1</th>
<th colspan="2">Major 2</th>
</tr>
<tr>
<th>col1</th>
<th>col2</th>
<th>col3</th>
<th>col4</th>
</tr>
</thead>
<tbody>
<tr>
<td>data1</td>
<td>data2</td>
<td>data3</td>
<td>data4</td>
</tr>
</tbody>
</table>