I'd recommend a nice little Windows program called Image Grabber. It's free and IMHO does a very nice job of creating single screen caps or a contact sheet from a vid. There are three versions. The latest is for Microsoft .NET only. If you don't have that, I'd recommend trying Image Grabber II (the one I've used). If all fails you can use their earliest version.
http://www45.brinkster.com/antworkz/