<script>
function mouseMove(ev){
ev = ev || window.event;
var mousePos = mouseCoords(ev);
document.getElementById('xxx').value = mousePos.x;
document.getElementById('yyy').value = mousePos.y;
}

function mouseCoords(ev){
if(ev.pageX || ev.pageY){
return {x:ev.pageX, y:ev.pageY};
}
return {
x:ev.clientX + document.body.scrollLeft - document.body.clientLeft,
y:ev.clientY + document.body.scrollTop - document.body.clientTop
};
}

document.onmousemove = mouseMove;
</script>

Mouse X Position:
<input id=xxx type=text>
<br>Mouse Y Position:
<input id=yyy type=text>