How can I condition which thread belongs to which forum?

[vexxy]

When I user visits a thread, I want to highlight the parent forum of the respective thread...what's the condition?

tnx in advance

edit: I found how can i condition if is a forum what forum belongs in the x parent forum with:

<vb:if condition="$foruminfo[forumid] == 'x' OR $foruminfo[parentid] == 'x'">

the problem is, if I visit a thread from that parent id, it acts wierd...it verifies the condition and the else branch...i'm puzzled

the forum structure is like this:

Forum A (parent)
- Forum B
-- Forum C

If I visit forum A, it's all good, if I visit forum B it's all good...forum C does not verify the condition (probably because can't verify the master parent condition). Any threads i visit from any of those forums, both verify and deny this condition...i don't get it.