This isn't the extension version, but there's a phpbb version, and installing this is plain-easy.
You can download the phpbb version here: https://frug.github.io/AJAX-Chat/
Anyway, it integrates this with your forum, so you don't need to manually add users.
But, is there any place over the ACP for any settings, or are the only settings inside the chat itself only?
Another question: Is there a way to keep the chat-history in the chat somehow?