just some guy,
Another link for you:
http://www.3danimatedwallpaper.com/
They say "Plays most screen savers on the desktop", but alas not the aquarium. It might however work with the XP version, because that one uses the preview mode (small monitor in the display settings) which is required for this program to display it on the desktop. I believe I have seen similar programs that also required the preview mode.
Jim,
I know some time ago you had not figured out how to get the preview mode working in directx 6. It seems not figuring this out is a good way to prevent people from running the aquarium on their desktops.