Scraping Ajax inner HTML

I'm trying to scrape a site whose second menu fetches its parameters with ajax based on the selection of the preceding drop-down. I've read what is written on the subject in earlier posts but I don't really understand how I will be able to pick the responses in a scrapable file. This is what the ajax part looks like:

//If ajax support
if(ajax){
//leave only one element as option, exclude the rest
document.formSearch.districtList.options.length = 1;

idOpcao = document.getElementById("opcoes");

ajax.open("POST", "district.php", true);
ajax.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");

ajax.onreadystatechange = function() {
//while processing... display message
if(ajax.readyState == 1) {
idOpcao.innerHTML = "Loading...";
}

//after processing - call function processXML that will fill the data
if(ajax.readyState == 4 ){
if(ajax.responseXML){
processXML(ajax.responseXML);
}else{
//If its not an XML file display the below message
idOpcao.innerHTML = "Select City first";
}
}

}
//get city code
var params = "city="+value;
//alert(params);
ajax.send(params);
}
}

function processXML(obj){
//get the city tag
var dataArray = obj.getElementsByTagName("district");

var sessionDistrict = "";

//total of elements in the city tag
if(dataArray.length > 0) {
//search the XML file to subtract the data
for(var i = 0 ; i < dataArray.length ; i++) {

var item = dataArray[i];

//content in the XML file
var codigo = item.getElementsByTagName("code")[0].firstChild.nodeValue;
var descricao = item.getElementsByTagName("description")[0].firstChild.nodeValue;

idOpcao.innerHTML = "Select a district";

//create a new option dynamically
var new= document.createElement("option");

//set an ID to the attribute
novo.setAttribute("id", "option");

//Begin selection of last search
if( description == sessionDistrict ){
new.setAttribute("selected", "selected");
}
//End selection of last search

//attribute a value
new.value = codigo;
//text attribute
new.text = descricao;

//add a new element
document.formBusca.District.options.add(new);
}
}
else {
//if the XML returns empy display message below
idOption.innerHTML = "Select city first";
}
}

----

And that's it. Any leads on how I can hook in a scrapable file given the above logic?

Best,
Johan