Hi Marten,
Apologies for the delay on this.
I think it might be a little tricky to achieve this especially since when you navigated to a post or a forum the box doesn't resize and would more than likely cut some of the post off.
If you want to try it you would need to edit the index.php file of the scroller and change a few of the settings:
$('link1'

.addEvent('click', function(event) {
event = new Event(event).stop();
scroll.toElement('content1'

;
});
Thats the code that makes the first link in the menu scroll to the first div called content1. Its really just behaving like an anchor so you could change content1 to the name of the anchor of the forum section/category in order to make it scroll to it.
The menu link would then be hardcoded into the menu then and would only be relevant if you were on that page - otherwise if the nachor you stipulate doesnt exist it will more than likely throw an error and stop the other items from working.
I think the idea sounds great but the script is a bit limited for that kind of application.
Anthony.