Shoutbox

code:

---

function OnEvent_ChatWndCreated(ChatWnd){
    ChatWnd.SendMessage("hello");
}

---

This does exactly what you are after.  If you wanted a different message then change hello.  To implement this then go into the Messenger Plus! Live preferences > General > Scripts > Create New... > Give it a name you want > OK > paste the code in the large box > OK > your script is now running.