Do not use overflow: hidden on the BODY element ESPECIALLY if all the children of the BODY element are being absolutely positioned.
Such elements are not in flow and thus do not effect the calculated height of the BODY element; and the browser should think the BODY element is not very tall; in fact shorter than the window.
Overflow: hidden complicates the matter by telling the browser to only show scrollbars if the BODY element is tall enough to need it.
See the CSS 2.1 Specification on the overflow: hidden value:
Perl / MySQL / HTML+CSS