// Detect if the browser is IE or not.
// If it is not IE, we assume that the browser is NS.
var IE = document.all?true:false;

// If NS -- that is, not IE, then set up event for mouse capture
if (!IE) document.addEventListener('mousemove', updateMouseXY, false);

// Set-up to use updateMouseXY function onMouseMove
document.onmousemove = updateMouseXY;

// X,Y-coordinate relative to the document topleft corner:
var mouseX;
var mouseY;

function updateMouseXY(e) 
{
  if (IE) { 
	// grab the x-y pos.s if browser is IE
    mouseX = event.clientX + document.body.scrollLeft;
    mouseY = event.clientY + document.body.scrollTop;
  } else {  
	// grab the x-y pos.s if browser is NS
    mouseX = e.pageX;
    mouseY = e.pageY;
  }  
  
  // catch possible negative values in NS4
  if (mouseX < 0) {mouseX = 0}
  if (mouseY < 0) {mouseY = 0}  
}