function ajaxInit() {
    var xmlHttp;
    try {
        xmlHttp=new XMLHttpRequest();
    }
    catch (e)
    {
        try {
            xmlHttp=new ActiveXObject("Msxml2.XMLHTTP");
        }
        catch (e) {
            try {
                xmlHttp=new ActiveXObject("Microsoft.XMLHTTP");
            }
            catch (e) {
                alert("Your browser does not support AJAX!");
                return null;
            }
        }
    }
    return  xmlHttp;
}

function retrieveModel() {
    var tmpMake = document.carform.Make[document.carform.Make.selectedIndex].value;
    //alert(tmpMake);
    if(tmpMake == "0") {
        var tmpOption = new Option("Select Make","0");
        document.carform.Model.options.length = 0;
        
        document.carform.Model.options[0] = tmpOption;
        return ;
    }
    var xmlHttp = ajaxInit();
    if (xmlHttp == null) {
        return;
    }
    xmlHttp.onreadystatechange = function() {
        if (xmlHttp.readyState == 4) {   
            if (xmlHttp.status == 200) {
                //alert(xmlHttp.responseXML.xml);
                var xmlDoc = xmlHttp.responseXML.documentElement;
                var obj = xmlDoc.getElementsByTagName("model");
                var objects = [];
                
                
                if (obj[0].getAttribute('status') == 'ok' && obj.length > 0) {
                    document.carform.Model.options.length = 0;
                    document.carform.Model.options[0] = new Option("Any","Any");
                    for (var i = 0; i < obj.length; i++) {
                        var tmpOption = new Option(obj[i].getAttribute("name"),obj[i].getAttribute("name"));
                        document.carform.Model.options[i+1] = tmpOption;
                    }
                                        
                } else {
                    var tmpOption = new Option("<---------","0");
                    document.carform.Model.options.length = 0;
                    
                    document.carform.Model.options[0] = tmpOption;
                    var tmpOption = new Option("Any","Any");
                    document.carform.Model.options[1] = tmpOption;
                }

            }
        }
    }

    var tmpMake = document.carform.Make[document.carform.Make.selectedIndex].value;
    var str = "Make=" + tmpMake;
    //alert(str);
    xmlHttp.open("GET","http://www.usedcarshowroom.co.uk/car_search_model.asp?" + str,true);
    xmlHttp.setRequestHeader("Content-Type", "application/x-www-form-urlencoded; charset=UTF-8"); 
    xmlHttp.send(null);

}