Welcome to the forums,
Web-client side the UI needs a bit more work, but if you're using an external XMPP client it's fairly straightforward.
Pidgin and Zimbra - Zimbra :: Wiki Spark and Zimbra - Zimbra :: Wiki Adium and Zimbra - Zimbra :: Wiki
After connecting, make a new persistent chatroom against the virtual conference.domain.com (New user's connecting will automatically get a replay of recent convo.)
Bug 21340 - Collaborative chat (aka chat rooms) (web-ui)
Bug 27700 - Enable conference room support from the IM code (admin configuration options)