In IE6 I don't see the content of the scroll layer. After some investigation I
noticed that the hieght of the "scrolled" layer was 0px. It turns out that
document.body.clientHeight is 95px. So you expression() returned a height of 0.
In IE6 in "standards" mode body.clientHeight returns the document. In your case
it's 95px and so the result will always be 0.