Stills from movies are known as frame grabs. This is because a movie is made up of 25 frames per second and you are grabbing one of those frames.
The best way to get a frame grab from movie maker is to use the video clip from the collections folder. This will give you a 640 x 480 sized picture. If you grab a still from the video clip after placing it on the timeline or storyboard you will get a picture 384 x 288. So, if you want as good a quality picture as you can get to say print off, use the video from the collections. If you want to email the picture or something similar, you may find taking it from the timeline saves you editing it to make it small enough to use.
Let's grab that still!! Watch the video tutorial here
With movie maker open and your video clip in the collections folder, click on the video file to highlight it. You will now see the video clip appear in the preview screen.
You now need to find the still you want to grab, so either click on the play button or use the seek bar under the preview monitor to find the approximate place you need to be and then the play or frame forward buttons for accurate placement.
To the right of the play button, at the bottom right of the preview monitor screen, you'll find a button which looks like it has a picture of a camera on it. This is the frame grab button. Click the frame grab button.
The save picture as window opens. By default it will show the my pictures folder as the location, but you can browse to wherever you like and then type in the name you wish to give the picture, if you don't want to use the default name of video clip name_000, which may not mean much to you after five minutes!
When you have done this, click Save and you are done. Movie Maker will automatically add the still picture to your collection.