practicality

I know a lot of people on my f-list make screencaps out of AVIs - any recomendations for good, free programs to do it with? My current method consists of finding the shot in VirtualDub, copying it to the clipboard, and then pasting in PSP and saving, which works when it's only one or two, but I've got a bunch of files to do a lot from, and there _has_ to be a simplier way. Help?