So you're using the MUS for your chatroom, or ... ? You might provide more details before getting antsy about the lack of response to your question.
Yeah my bad, i am using OpenSMUS to host the server.
And everything is made in Director 8.5.
You might perhaps send a message to the user/machine in question that, when received, will navigate the movie to the named marker. Which part of this are you having trouble with?
SendNetMessage(), GetNetMessage() or SetNetMessageHandler(), and go() are all commands that you might use to achieve this, along with BreakConnection()
However, it's not clear where you are trying to send this /kick command from. You will have a "control" movie constantly connected? If so then you might research the above commands; otherwise you should clarify.