Probably z-index issue with IE7

In IE7, only the top part of the menu shows up. After the "header" div is closed, and the "content" div starts, the content makes the menu invisible (see attached images).

Update: Fixed it by adding the following to ie7.css (zen-subtheme):

#page-wrapper {
    position: relative;
}
#navigation {
    position: relative;
    z-index: 2;
}