function dealResult()
{   
    var dobj = document.getElementById("divResult");
    dobj.innerHTML =  cobj.req.responseXML.text;
}

window.onload = function()
{
    //绑定Post发送xmlHttp事件到btnTestPost
    loadTestPost();
    //绑定Get发送xmlHttp事件到btnTestGet
    loadTestGet();
};

最后是.net处理xmlHttp的代码
.net 处理xmlHttp请求
public class DefaultHandler : IHttpHandler
    {
        protected XmlDocument _xmlResult;

        public void ProcessRequest(HttpContext context)
        {
            if (context.Request["T"] != null)
            {//GET xmlhttp测试
                context.Response.ContentType = "text/xml";
                XmlDocument xmlDoc = new XmlDocument();
                xmlDoc.LoadXml(string.Format(@"<time>GET:{0}</time>", System.DateTime.Now));
                xmlDoc.Save(context.Response.OutputStream);
                context.Response.End();
            }
            else
            {//POST xmlhttp测试
                context.Response.ContentType = "text/xml";
                XmlDocument xmlDoc = new XmlDocument();
                xmlDoc.Load(context.Request.InputStream);
                if (xmlDoc.DocumentElement.Name == "T")
                {
                    xmlDoc.LoadXml(string.Format(@"<time>POST:{0}</time>", System.DateTime.Now));
                    xmlDoc.Save(context.Response.OutputStream);
                    context.Response.End();
                }
            }
        }