Alright, this code works in Chrome and FF, but not IE (which is to be expected). Does anyone see anything wrong with this code that would render it useless in IE?

var waittime=400;
chatmsg = document.getElementById("chatmsg");
room = document.getElementById("roomid").value; 
sessid = document.getElementById("sessid").value;
chatmsg.focus()
document.getElementById("chatwindow").innerHTML = "loading...";
document.getElementById("userwindow").innerHTML = "Loading User List...";
var xmlhttp = false;
var xmlhttp2 = false;
var xmlhttp3 = false;
function ajax_read() {
if(window.XMLHttpRequest){
    xmlhttp=new XMLHttpRequest();
    if(xmlhttp.overrideMimeType){
        xmlhttp.overrideMimeType('text/xml');
    }
} else if(window.ActiveXObject){
    try{
        xmlhttp=new ActiveXObject("Msxml2.XMLHTTP");
    } catch(e) {
        try{
            xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
        } catch(e){
        }
    }
}
if(!xmlhttp) {
    alert('Giving up :( Cannot create an XMLHTTP instance');
    return false;
}
xmlhttp.onreadystatechange = function() {
if (xmlhttp.readyState==4) {
    document.getElementById("chatwindow").innerHTML = xmlhttp.responseText;
    setTimeout("ajax_read()", waittime);
    }
}
xmlhttp.open('GET','methods.php?method=r&room=' + room +'',true);
xmlhttp.send(null);
}
function user_read() {
if(window.XMLHttpRequest){
    xmlhttp3=new XMLHttpRequest();
    if(xmlhttp3.overrideMimeType){
        xmlhttp3.overrideMimeType('text/xml');
    }
} else if(window.ActiveXObject){
    try{
        xmlhttp3=new ActiveXObject("Msxml2.XMLHTTP");
    } catch(e) {
        try{
            xmlhttp3=new ActiveXObject("Microsoft.XMLHTTP");
        } catch(e){
        }
    }
}
if(!xmlhttp3) {
    alert('Giving up :( Cannot create an XMLHTTP instance');
    return false;
}
xmlhttp3.onreadystatechange = function() {
if (xmlhttp3.readyState==4) {
    document.getElementById("userwindow").innerHTML = xmlhttp3.responseText;
    setTimeout("user_read()", 10000);
    }
}
xmlhttp3.open('GET','methods.php?method=u&room=' + room +'',true);
xmlhttp3.send(null);
}
function ajax_write(url){
if(window.XMLHttpRequest){
    xmlhttp2=new XMLHttpRequest();
    if(xmlhttp2.overrideMimeType){
        xmlhttp2.overrideMimeType('text/xml');
    }
} else if(window.ActiveXObject){
    try{
        xmlhttp2=new ActiveXObject("Msxml2.XMLHTTP");
    } catch(e) {
        try{
            xmlhttp2=new ActiveXObject("Microsoft.XMLHTTP");
        } catch(e){
        }
    }
}
if(!xmlhttp2) {
    alert('Giving up :( Cannot create an XMLHTTP instance');
    return false;
}
xmlhttp2.open('GET',url,true);
xmlhttp2.send(null);
}
function submit_msg(){
nick = document.getElementById("chatnick").value;
msg = document.getElementById("chatmsg").value;
document.getElementById("chatmsg").value = "";
ajax_write("methods.php?method=w&m=" + msg + "&n=" + nick + "&room=" + room +    "&sessid=" + sessid + "");
}
function keyup(arg1) { 
if (arg1 == 13) submit_msg(); 
}
var intUpdate = setTimeout("ajax_read()", waittime);
var intUpdate = setTimeout("user_read()", 0);