asp.net http post接口的有关问题

asp.net http post接口的问题？
protected void btnLoad_Click(object sender, EventArgs e)
 {
  //入口地址为：http://125.208.3.12:8888/sms.aspx
  string url="http://125.208.3.12:8888/sms.aspx?action=overage&userid=1152&account=111&password=111";
  Response.ClearContent();
  Response.Write(Post(urll));
  Response.End();
 }
   

public string Post(string url)
  {
  string returnData = null;
  try
  {
  HttpWebRequest webReq = (HttpWebRequest)WebRequest.Create(url);
  webReq.Method = "POST";
  webReq.ContentType = "application/x-www-form-urlencoded";
  Stream postData = webReq.GetRequestStream();
  postData.Close();
  HttpWebResponse webResp = (HttpWebResponse)webReq.GetResponse();
  Stream answer = webResp.GetResponseStream();
  StreamReader answerData = new StreamReader(answer);
  returnData = answerData.ReadToEnd();

  }
  catch (Exception ex)
  {
  Response.Write(ex.Message);
  }
  return returnData.Trim()+"\n";
  }
现在的问题是它return是xml形式的string，我怎样得到它标签里边的值？还有如果post(string url)的url改为入口地址,那参数怎么办,这方法又该怎么写？小生不才,望同业好手指点迷经，小弟在线等.. 


------解决方案--------------------

C# code

byte[] byts = new byte[Request.InputStream.Length];
            Request.InputStream.Read(byts, 0, byts.Length);
            string req = System.Text.Encoding.UTF8.GetString(byts); 

            XmlDocument xml = new XmlDocument();
            Response.ContentEncoding = System.Text.Encoding.UTF8;
            Response.ContentType = "text/xml ";
            xml.LoadXml(req);
            XmlNodeList topm = xml.DocumentElement.ChildNodes;
            foreach (XmlElement element in topm)
            {
                if (element.Name.ToLower() == "row")
                {
                    //得到该节点的子节点
                    XmlNodeList nodelist = element.ChildNodes;
                    if (nodelist.Count > 0)
                    {
                        foreach (XmlNode el in nodelist)//读元素值
                        {
                            
                        }
                    }
           }
     }