I assume you'd like the subforums to show vertically, instead of horizontally (I can't get onto the linked site at the moment).
For a quick edit, if you open default.asp and search for "'If there are other sub forums place a comma inbetween". Edit the line below the above, to remove the comma and add a line break;
If strSubForums <> "" Then strSubForums = strSubForums & "<br>"
Also, search for "'If there are sub forums" and then edit the line below that to show;
If strSubForums <> "" Then strSubForums = "<br />" & strSubForums
If you want them to be 'tabbed' inwards, find "'Display the sub forum" and edit the line below that to show;
strSubForums = strSubForums & " <a href=""forum_topics.asp?FID=" & intSubForumID & strQsSID2 & """ class=""smLink"">" & strSubForumName & "</a>"
That's just a quick edit whilst on my lunch break, but it gives you a basic idea.