Instant Message Function(repost)

I need software that will allow me to create a group of instant message contacts and send them instant messages over the standard services (AIM, GoogleTalk/Jabber, Facebook Chat, Yahoo Messenger, etc.). This will not be used for spamming anyone, as such, I need the program to read incoming messages for 'START' and 'STOP' commands and add/remove people from the distribution list in real-time. You could think of this as a chat room where only the moderator can send messages. Additionally, I would like the ability to easily pre-pend text to the beginning of eac h message as well as a character counter telling me how long the message is. I think it would be easiest as a plug-in for Pidgin or Adium.