Getting Mouse Coordinates In Safari 1.3

I've been having an issue with Safari when it comes to getting mouse coordinates after clicking on an element - specifically the Y coordinate. For some reason, the 0 position is the bottom left corner of the window. The further down the page, the lower the number gets. This is crazy behavior - I have this stupid thing working in every other browser, but Safari.

My script is modeled after the standard Quirksmode script:

function doSomething(e)
{
var posx = 0;
var posy = 0;
if (!e) var e = window.event;
if (e.pageX || e.pageY)
{
posx = e.pageX;
posy = e.pageY;
}
else if (e.clientX || e.clientY)
{
posx = e.clientX + document.body.scrollLeft;
posy = e.clientY + document.body.scrollTop;
}
// posx and posy contain the mouse position relative to the document
// Do something with this information
alert(posy);
}

My test HTML is like so:

<br><br><br><br><br><br><br><br>
<input type="checkbox"
<br><br><br><br><br><br><br><br>
<input type="checkbox"

Any help?