Drupal site: Primary links disappear under search widget when wrapping

On Drupal site, using Firefox 2.0 (linux Ubuntu and Windows), upon resizing window (say to 800 x 600), the menu items on primary links wrap, but disappear under search widget. See screenshot.
With IE 6.0 on Windows, a similar effect is noted, except that the menu items do not wrap discretely (one by one) but rather disappear gradually under the logo as they collide with it. They wrap also, and also disappear under search widget.