Instead of using $forum[forumid], try using $foruminfo[forumid]. Maybe that will work instead. (Also, try it with and without single quotes around "forumid". I always forget if it needs the quotes in there or not!)

Also, are you editing the correct template? Do this - 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.

I did it with this code in forumhome:
<if condition="$show['lastpostinfo'] AND $forumid!=28">

I would like to know how to do this, but not replace with a blank space.

Instead, the last post column is filled by the latest post from one of the other sub-forums.