The settings look right. A small note: You probably do not need to add a match for class-identifier when you are matching on node_id. There is no other node with a different class identifier.
Look in your debug-output. Does it say: No template could be found for....
In that case you should clear your caches (template+content in the rightmenu of the admin interface), and it should work.
Now it works. I found out that the foldernode79.tpl had to be in: /www/design/forum/override/templates ...which I don't find very logical..since the default class I'm overriding for a node is in: /www/design/forum/override/templates/full/..
Why does an override for folder has to be under templates..and not under templates/full?
