JScript : Getting img X & Y

I've got an image, which act as a map and i need to find the coordinate relative to the img when user click on it.
I've successfully manage to get the document coord (x & y) but can't get the img coord, any idea ?

Code:

---

               
function GetCoord(e)
                {
                        var x = (navigator.appName.substring(0,3) == "Net") ? e.pageX : event.x+document.body.scrollLeft;
                        var y = (navigator.appName.substring(0,3) == "Net") ? e.pageY : event.y+document.body.scrollTop;
                        x = x - document.frmAjout.imgCarte.scrollLeft;
                        y = y - document.frmAjout.imgCarte.scrollTop;
                        document.frmAjout.txtCoordX.value = x;
                        document.frmAjout.txtCoordY.value = y;
                }

---

take a look here

http://developer.irt.org/script/326.htm

or

http://developer.irt.org/script/35.htm

Those scripts don't seem to work :(
I can get the screen x,y
But i'd like to be able to get the x&y relatibve to the images without submitting the form...
Like x = x - img.left
y = y - img.top

Then i got the img x & y


Thanks for the reply :)