philly's method sucks. there are much better ways of doing it, most cost money due to having to buy the software.
i actailly posted this question on snowest about a month ago, and someone responded with this program
http://www.squared5.com/ . go there and download it. when you pause it, you can fwd/rwd in slow motion to get the EXACT image you want.
with the program open...
1. file
2. open files (its the first option in the file menu)
3. find your video and open it
4. hit play (the middle button right under the video........this is also the pause button)
5. when you find an area where you want to "snap" your still image, pause it (you dont need to be on the EXACT still frame you want)
6. on the bottom, RH side of the video there is are buttons like this <> . those are forward and reverse, slow motion buttons. you can get the video stopped on your exact image
7. when you want to snap a still image, follow the next steps
8. file
9. export frame
10. when the box pops up, make sure you save it as JPEG, change it to the best picture quality, and change the location where you want the picture saved.
its about as easy as it gets. im far from being a computer genius, and i found it really easy