You need to edit the postbit template and wrap the info you wish to hide in a conditional i.e.
Code:
<vb:if condition="$thread[forumid] != 8888">THE POSTBIT CODE YOU WANT TO HIDE HERE</vb:if>
So we trick it basically. If the forum ID is NOT 8888 show this etc.
To specify several forums at a time use this:
Code:
<vb:if condition="in_array($forum['forumid'], array(1,2,3))">
<vb:comment>Show Nothing in forums 1, 2, and 3</vb:comment>
<vb:else />
Put the OLD code here or rather, the code you want to show in all other forums so you don't lose it.
</vb:if>