One little trick that works is to have a spacer.gif in the column you want to have a minimum width. kind of like
<table
width="100%" border="0" cellspacing="0" cellpadding="0">
<tr>
<td>blah blah blah .....</td>
</tr>
<tr>
<td>[img]/spacer.gif[/img]</td>
</tr>
</table>