Dvd screen caps?

[TheBang]

I use Snapz Pro. It costs money, but that's always been an indispensable tool in my arsenal.

kagenaki koe's suggestion of VLC is probably your best bet for free though. You should be able to use Grab, or the built-in screenshot (cmd-shift-3) on it.

Alternatively, you could do something like use Handbrake to rip the DVD, and then do a regular screenshot of the resulting Quicktime movie.