Try this in the header template, replace your
HTML Code:
<td align="$stylevar[left]"><a href="http://www.mysite.com/forum"><img src="http://www.mysite.com/forum/images/misc/mylogo.png" border="0" alt="" /></a>
With (cms would be the name of your cms script like content.php leave off the php!)
HTML Code:
<if condition="THIS_SCRIPT == 'cms'">
<td align="$stylevar[left]"><a href="http://www.mysite.com/forum"><img src="http://www.mysite.com/forum/images/misc/myNEWlogo.png" border="0" alt="" /></a>
<if condition="THIS_SCRIPT == 'calendar'">
<td align="$stylevar[left]"><a href="http://www.mysite.com/forum"><img src="http://www.mysite.com/forum/images/misc/myOTHERlogo.png" border="0" alt="" /></a>
<else />
<td align="$stylevar[left]"><a href="http://www.mysite.com/forum"><img src="http://www.mysite.com/forum/images/misc/mylogo.png" border="0" alt="" /></a>
</if>