Defeat Apple's Anti-DVD-Screenshot DRM
Apple disables the OS X screenshot capability while a DVD is playing, but there is a workaround.
Using terminal, type in this command.
Your mouse should turn into crosshairs. Now hit the space bar. Your mouse should now be a camera. Click the window the DVD is playing in. A file called "filename.jpg" will appear on your desktop.
Found here with many more options:
http://highschoolblows.blogspot.com/2005/11/take-screenshot-of-dvd-player-in-os-x.html
Using terminal, type in this command.
screencapture -i ~/Desktop/filename.jpg
Your mouse should turn into crosshairs. Now hit the space bar. Your mouse should now be a camera. Click the window the DVD is playing in. A file called "filename.jpg" will appear on your desktop.
Found here with many more options:
http://highschoolblows.blogspot.com/2005/11/take-screenshot-of-dvd-player-in-os-x.html