I'd need to play with this on a duplicated theme/mod or the live box. There is a lot of different templates/php changes there.
Do me a favor though
Code:
<td class="alt1Active" align="$stylevar[left]" id="f$forum[forumid]" width="33%">
Where you see width="33%" - that's the first line from the forumhome_forumbit_columncell template you posted up above - increase that width to say 50% and take a screenshot if it makes a different - let me know what it does.