XmlDocument doc = new XmlDocument();
            doc.LoadXml("<employeeclass><firstname> tom </firstname><lastname> wang </lastname></employeeclass>");
            XmlNode node = doc.FirstChild;
            XmlDocument doc2 = new XmlDocument();
            doc2.Load("c:\\a.xml");
            XmlNode root = doc2.SelectSingleNode("employees");
            XmlNode newNode = doc2.ImportNode(node, true);
            root.AppendChild(newNode);
            doc2.Save("c:\\a.xml");

------解决方案--------------------

//楼主参考下,看看是不是这个意思.
C# code


XmlDocument doc = new XmlDocument();
        doc.Load(Server.MapPath("Employee.xml"));
        XmlNode objectNode = doc.SelectSingleNode("employees");
        XmlDocumentFragment docFrag = doc.CreateDocumentFragment();
        docFrag.InnerXml = "<employeeclass><firstname>tom</firstname><lastname> wang </lastname></employeeclass>";

        objectNode.InsertAfter(docFrag, objectNode.LastChild);

        doc.Save(Server.MapPath("Employee.xml"));