I really want/need to get screen captures from a few dvds.
But the question is how does man do them?
Do I need a program or something?
Please help me

If printscreen doesn't work, get a copy of FRAPS - designed mainly for gaming, but it means that it can capture overlays, too.

supposing you have windows media player:

1. Open your Window Media Player and click Options on the Tools menu.
2. On the Performance tab, click on the Advanced... button.
3. Uncheck Use overlays from DVD video, click OK and restart the player.

press Print Screen (PrintScrn) key (or ALT + PrintScrn key). then paste the image into your image editor.

can anyone please suggest the easiest way to do them on a mac?

if you are using Quicktime:
pause the movie and take a screenshot (cmd + shift + 4, then select the area with the movie image).

if you are using Apple's DVD player:
download this program: http://www.efritz.net/software.html. You click the "snap" button, then move to the DVD window, click once and then when the cursor changes you drag to select the area, release, and it's done.