Problem with window out of alignment only on select MAC browsers - page is valid

I have an issue with select Macintosh browsers displaying this page here like you see in the screenshot attached to this post (news ticker overlaps the black image below it)

The page is validated in terms of XHTML and CSS, which was recommended I do first because I’ve heard that when you have troubles with pages in only certain browsers it’s best to begin with validation.

This page displays fine in these browsers:

PC versions of FF, IE, Opera, Chrome, Safari

and in the MAC version of Chrome.

But does not display properly in these browsers:

MAC versions of FF and Safari.

Any ideas?