What about:

<table summary="xx" style="width:800px">
<col style="width:100px"/>
<col style="width:50%"/>
<col style="width:2*"/>
<col style="width:3*"/>
<tr><td>alpha</td><th>beta</th><td>gamma</td><th>delta</th></tr>
</table>

alpha	beta	gamma	delta

Column widths should be 100px, 400px, 120px, 180px?

Incorrect in all browsers?

NO: proportional values not defined in CSS