dark_jedi said: will VDub take a single frame screenshot?
VirtualDubMod (which is what I'm using) will do. Try choosing "Video" from the top menu bar.
Beware those screencaps might not have square pixels. They'd be 720x480, or anamorphically squeezed in this case (unless you're taking them from your lossless .AVI which might be a different rez...)