guid.js

var TypeLib = new ActiveXObject("Scriptlet.TypeLib"),
    guid = TypeLib.Guid;

document.write(guid);

newGuid.js

function newGuid(){
    var guid = "{";
    for (var i=1; i<=32; i++){
        var n = Math.floor(Math.random()*16.0).toString(16);
        guid +=   n;
        if((i==8)||(i==12)||(i==16)||(i==20))
            guid += "-";
    }
    return guid+"}";
}