ie6下 ajax的回调函数问题

代码：var req;

function createXMLHttpRequest() {
if (window.XMLHttpRequest) {
req = new XMLHttpRequest();
} else {
if (window.ActiveXObject) {
req = new ActiveXObject("Microsoft.XMLHTTP");
} else {
alert("\u4e0d\u80fd\u521b\u5efaXMLHttpRequest\u5bf9\u8c61!");
}
}
}
function processHomeAddress1() {
var city = document.f1.city;
city.options.length = 0;
if (req.readyState == 4 && req.status == 200) {
var s = req.responseText;
var addrArray = s.split(":");
city.options[0] = new Option("\u57ce\u5e02", "0");
for (var i = 0; i < addrArray.length; i++) {
var cityArray = addrArray[i].split("x");
city.options[i] = new Option(cityArray[1], "" + cityArray[0]);
//alert(addrArray[i]);
}
}
}
function homeAddress1() {
var province = document.getElementById("province1");
var provinceVal = province.value;
if (req == null) {
createXMLHttpRequest();
}
req.onreadystatechange = processHomeAddress1;
req.open("GET", "cityList.html?id=" + provinceVal+"&"+new Date().getTime(), true);
req.setRequestHeader("If-Modified-Since","0");
req.send(null);
}
第一次发送异步请求，页面能正常显示返回的结果，第二次的时候，后台运行了第二次的请求，但是回调函数没有运行，结果不能显示，请高手解答！

req.open("GET", "cityList.html?id=" + provinceVal+"&"+new Date().getTime(), true);

get会有缓存的，楼主试试post方法？

改成POST依然不行，请高手指教

req.onreadystatechange = processHomeAddress1;
req.open("POST", "cityList.html?id=" + provinceVal+"&t="+new Date().getTime(), true);
req.send(null);