I think a forum that might encourage people to post is a questions forum. For anyone new or browsing it could be helpful if there was a specific place to ask things. Also a general chat forum, as previously suggested, will many times help create activity because people can 'socialize' and get to know one another. As they become friends and learn more about your products... they'll be more beneficial to the community at large. There is no guarantee when you create any new forum but different things are worth a try.
Sometimes changing some of the icons (new message, smilie or posting icons) can make a difference.
I did have to look for the message board links. They're not all worded the same nor in the same place but if others are finding them that is all that matters. (Some of the "feedback" links go to the forum and at least one other pointed to mediaramp.) It's just something I noticed.
