Here's a guide to capturing screenshots which any one of the many DVD player programs should be able to do. However, since we're cheap we need a free alternative and that is where Virtual Dub comes in. Virtual Dub is really a movie/AVI editing program but has a simple way to capture screenshots in the original size and aspect. To capture a screen in Vitual Dub all one has to do is seek to the time of the screenshot (CTRL+G, then enter the time) and then pressing CTRL+1 which will copy the screenshot to the clipboard. Then simply paste to MS Paint or something and save the image.
Aside: For those who want a bit more here are some video software that I found useful. First is Slysoft's CloneDVD2 which is intended to backup your DVDs but also makes perfectly good DVD format movies on your hard drive. After getting your movie backedup one can use Ahead: Nero Showtime to capture the screenshot from the movie using the built in feature.