<script type="text/javascript">
<!-- 
//Browser Support Code
function ajaxFunction(){
    var ajaxRequest;
    
    try{
        // Opera 8.0+, Firefox, Safari
        ajaxRequest = new XMLHttpRequest();
    } catch (e){
        // Internet Explorer Browsers
        try{
            ajaxRequest = new ActiveXObject("Msxml2.XMLHTTP");
        } catch (e) {
            try{
                ajaxRequest = new ActiveXObject("Microsoft.XMLHTTP");
            } catch (e){
                // Something went wrong
                alert("Givearn isn't supported by your browser!");
                return false;
            }
        }
    }
-->
<!--    
    // Create a function that will receive data sent from the server
    ajaxRequest.onreadystatechange = function(){
        if(ajaxRequest.readyState == 4){
            var ajaxDisplay = document.getElementById('ajaxDiv');
            ajaxDisplay.innerHTML = ajaxRequest.responseText;
        }
    }
    ajaxRequest.open("GET", "is_online.php", true);
    ajaxRequest.send(null); 
}

-->
   setInterval(ajaxFunction, 1);
   </script>

It's not working in IE... works like a charm in FF

does it;

not do anything?
do something but not what you expect?
give errors?

or something else?

In IE it does nothing and doesn't give any errors