I launched you page in IE6 and the navigation definitely disappears when the browser resize effects the width of the window (it doesn’t do it if you only change the height).
Some Drupal developers had a similar issue with their sidebar disappearing in IE6 and they were able to fix it. I saved off your source and added the following CSS:
Code:
#header_container {
_zoom: 1;
}
This seems to fix the problem (although I don’t know what it does). Here’s the post from the Drupal forum: http://drupal.org/node/220551 (look at comment #3).
Hope that helps. If you see any hot-linking requests in your server logs, that’s me; I hot-linked all your stuff to test that change.