Group chats in bitlbee using most Jabber servers
See GtalkGroupchats for Google Talk accounts specifically.
1. First of all, add the account if you haven't already, eg:
account add jabber me@myjabberserver.com [password]
2. Then add the chatroom using the chat add command. Most jabber room names take the form roomname@conference.server.
chat add [account] myroom@conference.myjabberserver.com
You can optionally append a different name for the channel to be created; it will default to the room name.
3. Join the channel now associated with the group chat (chat list if you are unsure)
/join #myroom