in FORUMHOME and FORUMDISPLAY templates find:
Code:
<td class="thead" width="100%" align="$stylevar[left]">$vbphrase[forum]</td>
<td class="thead">$vbphrase[last_post]</td>
and Replace it with
Code:
<td class="thead" width="65%" align="$stylevar[left]">$vbphrase[forum]</td>
<td class="thead" width="35%">$vbphrase[last_post]</td>
change width
65+
35=
100 to what ever fit to your forum
Regards