Sure. While the page itself doesn't validate (mainly errors of the validator trying to parse javascript), the column sections do validate.
<table>
<colgroup span="2" class="monkey"></colgroup>
<colgroup span="3" class="potato"></colgroup>
<tr>
<td>HTML</td>
<td>should</td>
<td>always</td>
<td>play</td>
<td>nice</td>
</tr>
</table>
This would create a table with 5 columns in a single row, the first two set to the class monkey, the next the set to the class potato. So 'HTML' and 'should' would display according to monkey, while 'always', 'play', and 'nice' would display according to potato (works with other things, fonts, etc, just an example). These attributes would also be assigned to the same columns in any additional row.
Doesn't work in Konqueror or Safari... and I don't think it works in Mozilla either, but it does in IE. *shrug*