As far as I can tell, NextGen is broken when used with the standard Twenty Ten theme and IE 7. If one adds the most vanilla shortcode possible: [gallery=1] on a page or post, you get rows/columns of thumbnails of the images in the gallery. But the problem on IE 7 is that if you try to look at your menubar, the submenus (#access ul ul in the Twenty Ten style.css) are displayed under the gallery thumbnails.
Adding other images (say from the media gallery) work just fine - they don't cover the submenus.
Given that Twenty Ten is the standard WP 3 theme, it should be considered the gold standard by which bugs are judged - thus this must be considered a NextGen bug. While IE 7 is obsolete, it is still used by a very significant fraction of the viewing public, and still needs to be supported.
Is there a work around for this? NextGen should be fixed so that it supports Twenty Ten, but is there a CSS workaround for the thumbnails? Given regular images work, there must be something in the NextGen thumbnail CSS that is breaking IE 7. Even a
<!--[if IE 7]> type solution would be helpful.
(I tried to search both in NextGen and Twenty Ten for a solution for this, but could not find the right combination of search terms that showed a solution. Sorry if this is redundant.)