This will only work in Safari on Mac OSX, but it would be possible to create fallback methods for other browsers by rendering the composition to a movie, and set up a combo of JavaScript and HTML to load one or the other depending on platform and browser:
Screensaver by Aaron Welton
<embed type="application/x-quartzcomposer"
src="my_composition.qtz"
id="myComposition"
width="300px"
height="150px"
opaque="false">
</embed>
