You should be able to do this by placing the code in the template, I have not touched vb5 honestly, but looking at a bit from one of yil's products it looks like conditionals are the same as vb4
Code:
<vb:if condition="$vboptions['yilmazhidetextfromguest_on'] AND ($user['userid'] == 0)">
So would it be something like
Code:
<vb:if condition="$foruminfo['forumid'] == 2">CODE FOR FORUM 2 (background video with CSS cover)</vb:if>
No idea how templates are but I would think they kept it (sort of) similar so whatever would be the forum display template?