bgscreensaver is a simple AppleScript program to start and stop a screensaver module as a desktop picture. The original shell command for this trick is courtesy of Micheal Conwell (as reported by Michael Coyle at ResExcellence.com)
ANONYMOUS This application works exactly as described. While I seriously doubt that I would want to keep a screensaver/animated background enabled all the time, it's a neat little toy and a fun way to demonstrate the power of the Quartz subsystem to curious folks. (Version 1.1)
PAUL The application doesn't run on my computer (10.2.8), but the applescript itself works perfectly... and does exactly what I expect it to do.
I don't know if there is an exported interface that you could use to do this, but it would be nice to be able to choose which screen saver to use as the desktop. (Version 1.0)
GUARDIAN ARCHON If you like this and you'd like to do something similar, check out Quartz Desktop. It allows you to put .qtz files on your desktop. This includes Apple screensavers such as the RSS Visualizer and Spectrum.