The GUI is not definitive, but it helps us work, and is beautiful enough to be shown ;)
this screenshot shows you the main global options of the applications. It permits you to figure out what you can expect for such a project.
On top left you can see the buddy List, it's the list of your friends, you can add/remove contacts and see if they are present/away/busy...
There is a tab for each opened chat room. On the bottom right you can see the list of connected users. you can change your nickname online, and can, as you can see on next screenshot, access several options if you are the owner or moderator of this room.
This menu is more or less complete depending on your status it the current chatroom.
The room owner have access to the room configuration form, which is dynamically build. All available options are displayed, depending on the server configuration.
Here is the final screenshot, the private chat window. You can chat with a buddy friend (a jabber contact) or/and a chat room user.