Why not just use IRCNet for example? (It is probably one of the most popular ones, along with maybe QuakeNet and some others)
It should be pretty easy to use through http://webchat.xs4all.nl/ if people don't want to install clients like mIRC or something else.
Just choose IRCNet as the network, put a nick (it might require you to change it if it is in use already by someone else), choose Other from the chatchannel list, and then put the other chatchannel as #SWDB (for example).
IRCNet (and it is the same with all other networks/servers as far as I know?) doesn't keep the channel on though if there is nobody there.... so once everybody leaves the channel goes away and can be claimed by anyone. But I'm usually online 24/7... well I usually just idle and don't speak but... yeah.
Live chats like IRC might move the conversations away from the forum though.