ok, provalo un po'
codice:
<script type="text/javascript" language="JavaScript">
<!--
function getMousePosition(e){
	if(!e) e=window.event;

	var vDoc=(document.documentElement && document.documentElement.scrollTop)?document.documentElement:document.body;

	var mouseX=(e.pageX)?e.pageX:e.clientX+vDoc.scrollLeft;
	var mouseY=(e.pageY)?e.pageY:e.clientY+vDoc.scrollTop;

	alert(mouseX+','+mouseY);
}

if(document.layers) document.captureEvents(Event.CLICK);
document.onclick=getMousePosition;
//-->
</script>
ciao