function getXmlHttpPrefix() {
    if (getXmlHttpPrefix.prefix)
        return getXmlHttpPrefix.prefix;
    
    var prefixes = ["MSXML2", "Microsoft", "MSXML", "MSXML3"];
    var o;
    for (var i = 0; i < prefixes.length; i++) {
        try {
            // try to create the objects
            o = new ActiveXObject(prefixes[i] + ".XmlHttp");
            return getXmlHttpPrefix.prefix = prefixes[i];
        }
        catch (ex) {};
    }
    
    throw new Error("Could not find an installed XML parser");
}

//////////////////////////
// Start the Real stuff //
//////////////////////////


// XmlHttp factory
function XmlHttp() {}

XmlHttp.create = function () {
    try {
         if (window.ActiveXObject) {
            return new ActiveXObject(getXmlHttpPrefix() + ".XmlHttp");
        }
        else  
        if (window.XMLHttpRequest) {
            var req = new XMLHttpRequest();
            //some versions of Moz do not support the readyState property
            //and the onreadystate event so we patch it!
            if (req.readyState == null) {
                req.readyState = 1;
                req.addEventListener("load", function () {
                    req.readyState = 4;
                    if (typeof req.onreadystatechange == "function")
                        req.onreadystatechange();
                }, false);
            }
            
            return req;
        }        
    }
    catch (ex) {
    throw new Error("Your browser does not support XmlHttp objects");
    }
}

function _startLoadXmlTree(url) {
    var xmlHttp = XmlHttp.create();
    if (xmlHttp.overrideMimeType){
        xmlHttp.overrideMimeType("text/xml; charset=UTF-8");
    }
    xmlHttp.open("GET", sSrc, true);    // async

    xmlHttp.onreadystatechange = function () {
        if (xmlHttp.readyState == 4) {
            alert(xmlHttp.responseText); //可以取得xml的内容?????????????
                        alert(xmlhttp.responseXML.documentElement); //为空???????????
        }
    };
    // call in new thread to allow ui to update
    window.setTimeout(function () {
        xmlHttp.send(null);
    }, 10);
}

<?xml version="1.0"  encoding="UTF-8"?>
<tree>
<tree text="MH" src="GuideList/MH.xml"/>
<tree text="MR" src="GuideList/MR.xml"/>
<tree text="a.swf" action="JavaScript:Play('player.html?file=file:///D:/Test/Guides/Flash/a.swf')"/>
<tree text="cc.swf" action="JavaScript:Play('player.html?file=file:///D:/Test/Guides/Flash/cc.swf')"/>
<tree text="movie_name.swf" action="JavaScript:Play('player.html?file=file:///D:/Test/Guides/Flash/movie_name.swf')"/>
</tree>