doesn't MS have tools to make a normal EXE an activeX plugin? If so why not make the aquarium an activeX and embed it in an HTML? this way you could use it as active desktop. just an idee, may be totally wrong with this!
and I found I site about games that use yuv overlay (like some DVD Players (and winamp) Maybee they can help you Jim to find a way to get overlay working!
www.libsdl.org/