You can make DVD movies play on the desktop while you work, without the need for any third-party software whatsoever. Here's how:
1. Open Apple DVD Player
2. From the "Video" menu, choose "Present Video on Screen"
3. Move the pointer to the lower right corner of the screen out of view
4. Take a screen shot using "Command-Shift-3." This will create a SimpleText document titled "Picture 1" at the root level of your hard drive.
5. Open the "Appearance" control panel or "Control-Click" on the desktop and choose "Change Desktop Background…"
6. Open up your hard drive and drag "Picture 1" to the open "Appearance" window or click on "Place Picture…" to choose the image, then click on "Set Desktop."
7. Return to Apple DVD Player and start your movie. Choose "Hide Apple DVD Player" from the Application Menu, and the movie should now play on the desktop.
On a PowerBook G3/400 with 128 MB RAM, running Mac OS 9.0.4, the movies have a tendency to be a bit choppy when you are performing other tasks, but they perform just fine otherwise, and it's kinda cool to see too!