Try as I might, I can't find any program that'll grab from a video file properly, and I can't find these anywhere.
Lt. Kroker, i use a program called "VirtualDub"
It's freeware, it's easy to use, and it does a bunch of other stuff too.
To get a framegrab out of it,
1. Open the file
2. Find the frame by dragging the prograss bar and using the left and right keys,
3. Then click the 'Video' menu and 'Copy source/output frame to clipboard'
4. Open a image program, paste it, save it.
I'm pretty sure it works for DVD's as well, but i havent got a DVD drive so i can't check... http://www.digital-digest.com/dvd/downloads/virtualdub.html
Anyways, hope that helps your situation.