DVD players

Hi,
I have a DVD drive, and have tried using a few different software players. They work, which is good. How would I go about screen-capturing, though? whenever I do, the area of the DVD is just blank. If the DVD is still playing, the movie continues to play in the captured image - If that makes sense?

How can I simply take a screen shot of a DVD movie?

Am I just using the wrong codec?

Thanks