VLC will not open this DVD.

That's a bummer. http://forums.cnet.com/7723-7582_102-524299/how-to-take-screen-captures-in-apple-s-dvd-player/ covers this issue and VLC to the rescue every time.

If the DVD has heavy copy protection then it can fail on VLC but you could research how to RIP the DVD so you can play it with VLC. But I will not discuss ripping.
Bob