Cual es el error?

[jesusito]

Hola a todos tengo el siguiente codigo:

function createRequest(){
var httpRequest = null;

if(window.XMLHttpRequest){//mozilla, safari,...
httpRequest = new XMLHttpRequest();

if(httpRequest.overrideMineType){
httpRequest.overriderMineType('text/xml');
}
} else if(window.ActiveXObject){ //IE
try{
httpRequest = new ActiveXObject("Msxml2.XMLHTTP");
}catch(e) {
try{
httpRequest = new ActiveXObject("Microsoft.XMLHTTP");
} catch (e) {}
}
}

return httpRequest;
}

function CargarCombo(objetoCombo,accion){

clearChildNode(objetoCombo);
http = createRequest();
http.open('POST', accion, false);
http.onreadystatechange = handleHttpGet;
http.send(null);

var select = document.getElementById(objetoCombo);

var items = http.responseXML.getElementsByTagName("Dato");
alert();
for (var i = 0; i < items.length; i++){

valueCombo=items.getElemenstByTagName('valor').ite m(0);
captionCombo=items.getElemenstByTagName('nombre'). item(0);
agregarDatosCombo(select, valueCombo, document.createTextNode(captionCombo));
}

}

function handleHttpGet(){

if (http.readyState == 1){

if(document.getElementById("wait")){
document.getElementById("wait").innerHTML ="Cargando Datos...";
document.getElementById("wait").style.visibility=' visible';
}
}

if (http.readyState == 4) {
if (http.status == 200){
}
if(document.getElementById("wait")){
document.getElementById("wait").style.visibility=' hidden';
}
}

}
/************************************************** ************************************************** ********************/
function agregarDatosCombo(select, valueCombo, captionCombo){
var opt;
http = createRequest();
opt = document.createElement("option");
opt.value = valueCombo;
opt.appendChild(captionCombo);
select.appendChild(opt);
}

function clearChildNode(elemID){
http = createRequest();
var elem = document.getElementById(elemID);

while (elem.childNodes.length > 0) {
elem.removeChild(elem.firstChild);
}

var opt;
opt = document.createElement("option");
opt.value = -1;
opt.appendChild(document.createTextNode('Seleccion e'));
elem.appendChild(opt);

}


pero me sale error, dice q http no es una propiedad


porq?

saludos