Google Map API V3: Parsing an XML document

I'm trying to update my Google Maps API web application that I had running fine under version two. Version three seems not only to have broken everything but also has placed the burden of writing one's own versions of a lot of missing API functions that are no longer there.

Soooo, what was a relatively simple adaptation of their "store locator" example under version two has turned into a gigantic headache.

More specifically, my problem is parsing the XML document that my PHP/mySQL code returns after the user has entered some data into the web page and sent it off to the server. I know that the test data that I've been entering works because, 1. it worked flawlessly under V2, and 2., If I hardcode it into the PHP page and then load that page I get the expectant XML document loaded in my browser (Firefox 3.6.13 running on Snow Leopard).

Update: After very careful tracing with Firebug I've discovered that "downloadUrl" function from here is returning the data correctly.

However, it looks like the function "GXml.parse(data)" ( from here) isn't processing the returned XML. I'm pasting that code below:

    function GXml(){}
GXml.value=value;
GXml.parse=parse;

function value(node){
     if(!node){
            return"";
     }
     var retStr="";
     if(node.nodeType==3||node.nodeType==4||node.nodeType==2){
            retStr+=node.nodeValue;
     }else if(node.nodeType==1||node.nodeType==9||node.nodeType==11){
            for(var i=0;i<node.childNodes.length;++i){
                 retStr+=arguments.callee(node.childNodes[i]);
            }
     }
     return retStr;
}


function parse(textDoc){
     try{
            if(typeof ActiveXObject!="undefined"&&typeof GetObject!="undefined"){
                 var b=new ActiveXObject("Microsoft.XMLDOM");
                 b.loadXML(textDoc);
                 return b;
            }else if(typeof DOMParser!="undefined"){
                 return(new DOMParser()).parseFromString(textDoc,"text/xml");
            }else{
                 return Wb(textDoc);
            }
     }
     catch(c){
            P.incompatible("xmlparse");
     }
     try{
            return Wb(textDoc);
     }
     catch(c){
            P.incompatible("xmlparse");
            return document.createElement("div");
     }
}

function P(){}
P.write=function(a,b){}
;P.writeRaw=function(a){}
;P.writeXML=function(a){}
;P.writeURL=function(a){}
;P.dump=function(a){}
;P.incompatible=function(){}
;P.clear=function(){}
;

function Wb(a){
     return null;
}