If you open the video file in VLC (http://www.videolan.org/vlc/) there will be a snapshot option under the Video dropdown menu. It'll be saved in My Pictures if you're on a Windows PC. The default file format is png.
Most QuickTime movie files can be opened in VLC, but apparently some can't (I'm yet to find one myself)
Thank you, Baylist, that works great. I�ve got some avi files I want to do the same with too and I can see the video but can�t hear the sound? Any ideas please?
Many thanks, I gave up and just uploaded them to photobucket as they were and whatever wizardry they have sorted it all out anyway and they work fine on there!?