Which template needs to be edited for thread column

[forumrunt]

AS title reads, I have successfully been able to add a column to the right of the FORUMHOME, and FORUMDISPLAY templates..

<table width="100%">
<tr><td valign="top">**FORUM**</td><td width="200px" valign="top">**BANNER**</td></tr>
</table>

But for the life of me I can't work out how to make the same edit so I can add a column next to posts in a thread, i.e.(view attachment)

Thanks in advance for any help.