http://www.cesoft.com/products/translucy.html

For users looking for a novel program that allows them to watch DVDs on their computers while working on other applications, Trans Lucy 1.0.1 may be just the thing. The application lets users float the video display above other applications, effectively allowing them to make the video display translucent. It should be noted that the application can only work with computers that have video cards that support Quartz Extreme, and that this is in fact a demonstration version. Users may use this version indefinitely, but only for 20 minutes at a time. Trans Lucy 1.0.1 is compatible with all systems running Mac OS X 10.1 or higher. [KMG]