I've seen a few threads about various chat rooms, so I thought I'd take a crack at it. Why not start an IRC room? It's honestly not as hard as people make it out to be when it comes to moderation. A site like this would probably have what, 20-30 members on the irc channel? If that? There are various clients like pidgin (yeah yeah, i know...pidgin...) that let you log onto various IMs and IRC. So you could use the same client for MSN as IRC.

I would recommend mibbit for an in browser link, it's not that great of a client, but it's great for casual users. If I'm online (which is a lot) I'm on irc. It's great for lurkers like myself lol but really, setting up a room on a server, making a mibbit link and setting up the widget takes all of 20 minutes.