Interesting to note that the site is running on an AS400 - hmm, haven't seen one of those around for awhile.
Page layouts are simple with navigation nicely presented at top and bottom of each page.
The search function is a must on a site of this size - a site map would also add to the usefulness as we are at the mercy of the authors as too which heading they file pages under. Content is very full - and I guess quite scary to see the depth and breadth of what's available.