[veenuisthebest]

try this :-

Find this in header template

<td align="$stylevar[left]"><a href="$vboptions[forumhome].php$session[sessionurl_q]"><img src="$stylevar[titleimage]" border="0" alt="$vboptions[bbtitle]" /></a></td>

Replace with this:-

<if condition="$forumid == X">
<td align="$stylevar[left]"><a href="$vboptions[forumhome].php$session[sessionurl_q]"><img src="your image.gif" border="0" alt="$vboptions[bbtitle]" /></a></td>
<else>
<td align="$stylevar[left]"><a href="$vboptions[forumhome].php$session[sessionurl_q]"><img src="$stylevar[titleimage]" border="0" alt="$vboptions[bbtitle]" /></a></td>
</if>

Replace X with forum ID where you want a different logo. Not tested, but I hope it works !!