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There are about a million ways to pull stills from a video file, but they're going to be limited in their utility for printing. At maximum resolution, your DSLR's outputting 2 megapixels, and that's assuming you're not shooting interlaced. Then there's shutter speed, which when shooting video is typically going to result in really soft stills.
Pretty much anything that can edit video (and many things that can play video) can pull frames. QuickTime, FCP, VLC... In a pinch, you can just take a screenshot of a playback application.