tables/mozilla/core/table_widths.html

table width includes border
<hr align=left style="width: 200px;">
<table width=200 border=10>
 <tr>
  <td>200 table</td></tr>
</table>
<BR>

nested table width includes border
<table cellspacing=0 cellpadding=0 border>
 <tr>
  <td>
   <table width=200 border=10>
    <tr>
     <td>200 nested table</td></tr>
   </table></td></tr>
</table>

nested table width includes border
<table cellspacing=0 cellpadding=0 border>
 <tr>
  <td>
   <table width=100% border=10>
    <tr>
     <td>100% nested table</td></tr>
   </table></td></tr>
</table>