Creating a forum plugin wouldn't be too difficult. And there has also been some discussion about not limiting the discussions in Elgg community just to groups:

http://community.elgg.org/discussion/view/1072212/discussion-vs-groups

found a way to delete posts on hypeforum, only problem is it allows anybody to delete anybodys posts, now to fix that and i will be happy

any help on my last post would be greatly appreciated, as i no what not i do