I don't know anything about MS Authentication, but I thought I'd throw my suggestion in.

I've been using phpBB2 all this summer and have been amazed by its quality. It's not as easy to configure as it is with a full control panel in something like UBBThreads, but it's still pretty darn easy, and it's free of course.

There doesn't appear to be an official chat function yet. However, there are people out there actively creating mods and add-ons to the board, of which I've installed quite a few. There appears to be several developers of chat programs or chat interfaces for the phpBB software.

leftyfb, I think I understand what you're talking about in Ikonboard, but that's certainly not a chat. That's more like the private messaging function. Sort of like memos in an inbox. Plus, and correct me if I'm wrong, but you can only carry on a "conversation" like that with one other person.

That's another thing, are you requiring a two-member chat, or a chat room? Do you have to have multiple chat rooms?

Anyway, phpBB continues to amaze me in its value. I had UBBx with Infopop hosting for about a week. I hated it, it was insanely expensive, and just not worth it. It was also slow. phpBB has been quite fast, is completely free, and in my opinion is a better program all around than the UBB. Hell, I'm sorry to say it, but I like it better than this board software. But that's mainly because I never use threaded mode.