For starters the system is called IRC.
mIRC is a client for IRC
common mistake to new people.
Second, IRC is a proven multi-chat system, Messenger, Yahoo and the like aren't really design with multi-user chatting in mind.
They are no good for anything more then 5 people chatting, even then its annoying, they are really 2 person chat systems, with multi chat just thrown in there without any thought to its implemtation.