Well, here’s a weird one. Position an element relatively within a div set to scroll (auto, scroll) and the relatively positioned element behaves like a fixed element in IE (both 6 and 7). Taking advantage of that fact could get position:fixed working in IE6! But if you DON’T want that behavior, the work-around is to set the position of the scrolling div to relative as well.
Internet Explorer is a never ending source of surprises. Grrrrrr.