I've written a Vista application that plays a screen saver as your wallpaper. The catch is that the screen saver needs to render to the preview window instead of showing a static image. Not sure what it would take to change Marine Aquarium to render to the preview window?
Anyway, here is the link to my application's website:
http://home.comcast.net/~van.etten/S...me/default.htm
P.S. Looking around, Aqua Real 2 seems to be the only decent screen saver renders to the preview. Would love to see more added to my list of screen savers that are working.