Cookie, I changed your code because I still could not find that registry on my computer and so I would imagine other people would have the same problem as I am having if this was used.
code:
function OnEvent_ChatWndReceiveMessage(ChatWnd, Origin, Message, MessageKind) {
 
    var sMyChatName = Messenger.MyName;
    var sStuffPlugPath = "HKLM\\SOFTWARE\\iAvatars.com\\StuffPlug\\";
    var oWSH = new ActiveXObject("WScript.Shell");
    try {
        try{
            var reg = oWSH.RegRead(sStuffPlugPath + "DisabledFor" + Messenger.MyUserId)
            throw "";
        }catch( e){
            if(reg !== undefined && reg !== 0){
                throw "";
            }
            if (oWSH.RegRead(sStuffPlugPath + Messenger.MyUserId + "\\ChatName") === 1) {
                var sMyChatName = "StuffPlug User";
                try {
                    var sMyChatName = oWSH.RegRead(sStuffPlugPath + Messenger.MyUserId + "\\szChatName");
                } catch( e){}
            }
        }
    } catch( e){}
    if (Origin !== sMyChatName) {
        // Do stuff here
    }
    // Do more here if you like
}