First you find the template you need to add the text to. to do that - vboptions > General Settings > Add Template Name in HTML Comments > set to Yes . Then go back to your page and view the source code and you will see the name of the template called around your part of the code. Sometimes the template is the one mentioned at the very top of the page source.
Then add a condition in the template:
HTML Code:
<if condition="$forumid == 'x'">
text to add for forumid x
</if>