Mouse position

The following code gives the position of the mousepointer in het current cell where the mousepointer is in on that moment.

function document.onmousemove() {
alert(window.event.x + ', ' + window.event.y);
}
  But how can I retreive the REAL mouseposition. So NOT related to the current cell where mousepointer is in. ????

Never mind. Got it.
I should have used window.event.clientX