I Admin a very large community for writers; Absolutewrite.com/forums. The software is actually decent; it's not cheap. vBulletin from Jelsoft. If you can FTP and read, you can install vBulletin. We're running an older version; I have the current version on a test forum so members can get used to it before we change their world. The non-forum parts of vBulletin are ridiculous, for the most part, but the boards are quite flexible. But what makes the forum work, much as what made forums I've adminned for instruction, is active moderation. Good moderation encourages conversation. Good moderation tools help with that.