You have your xmlhttp.send(""); in the wrong place.
code:
var xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
xmlhttp.open("GET", "http://www.darksignsonline.com/chatlog-light.php", true);
xmlhttp.onreadystatechange=function() {
if (xmlhttp.readyState==4) {
Debug.Trace(xmlhttp.responseText);
}
}
xmlhttp.send('');