you can use Ultimate S to do it - they have a section that will frame grab each frame of your video and name it sequentially. You can manually do it by hitting the Save screen shot each frame and naming it.
I think Excalibur does it too, but I dont know for sure.
Irfanview also has an "extract all frames" option. You end up with bmp files but you can use Irfanview again to batch convert to any other image format. I just tried this with a 49 MB mpeg-2 clip and it did it in about 2 min.