WP-Forum-Server is basically an instant Mingle forum without so many options and less initial setup time!
Unless you want to go the Mingle paid plugins route, I'd advise you move to bbpress or simple-press. Also there are much more plugins and themes compatible with bbpress compared to simple-press. If you want to build your own forums module by module use bbpress. If you're already using buddypress find a good forum integration plugin at buddypress.org! If you want an out of the box solution and don't mind the initial setup time, simple-press is the way to go.
There are other forum plugins, but the ones I mentioned are definitely the best. Personally, I like simple-press. It should do everything you need a little more easily than bbpress, since developers codes can conflict in some cases with buddypress and bbpress, while simple-press is pre-packaged!
Hope this helps!