I just tried it on my G5 running IE 5.23 on OS 10.3.9 and it wasn't working. The main dynarch.com site simply stays at the please wait animated area where the menu should be. Additionally I tried opening most of the examples included in the download and was unable to view the menu (either no indication of the menu or the simple tree of the menu items in list form)

That being said, since MS is no longer developing IE for the Mac, I would only be worried about compatibility with Safari and Firefox, both of which work well with the menu.

Hope this helps,
-Kirk