This is the way I did it, you can modify it to suit your own needs
Add at the top of the HEADER template:
Code:
<table width="100%" border="0" cellpadding="0" cellspacing="0" background="yourdir/bg.gif">
<tr>
<td width="286" rowspan="2" valign="top"><a href="$vboptions[forumhome].php?$session[sessionurl]"><img src="yourdir/logo.gif" border="0" alt="$vboptions[bbtitle]" /></a></td>
<td width="100%" align="right" valign="top"><img src="yourdir/right.gif" width="36" height="100"></td>
</tr>
</table>
In the code the:-
yourdir/bg.gif is the background usually only a couple of px wide
yourdir/logo.gif the main logo as wide as you like
yourdir/right.gif this doesn't need to be too wide, just finishes of the right hand side