You should just be able to replace
Code:
<td align="$stylevar[center]">
<a href=""].php$session[sessionurl_q]">
<img src="$stylevar[titleimage]" border="0" alt="$vboptions[bbtitle]" />
</a>
</td>
with the your image information.
For example, here's mine:
Code:
<td width=50% class="headerlogo">
<a href="$vboptions[forumhome].php$session[sessionurl_q]">
<img src="images/yourheaderimage.jpg" align="left" style="border:none;" width="654" height="119" alt="alt text here" />
</a>
</td>