How can I return xml from a webservice instead of a dataset?

I am trying to load my data that I get from the db as a dataset into xml so i can return it and work with it in Flash.  How can I do this?  (it is a webservice)

[WebMethod(Description = "Return all employees in the database as xml.")]
    public XmlDocument GetAllPeopleRelXML()
    {
        ConnectionStringSettings setting = ConfigurationManager.ConnectionStrings["EmployeeConnectionString"];
        string constring = setting.ConnectionString;

        dsEmployee ds = new dsEmployee();
        SqlConnection conn = new SqlConnection(constring);

        conn.Open();

        dsEmployeeTableAdapters.spSelPersonAllRelTableAdapter personDA = new dsEmployeeTableAdapters.spSelPersonAllRelTableAdapter();

        personDA.Connection = conn;
        personDA.Fill(ds.spSelPersonAllRel);
        XmlDataDocument datadoc = new XmlDataDocument();
        ds.WriteXml(datadoc);

        return datadoc;
    }