The speed on your video clip is an important factor to look at when you are in your non-linear video editing software. The same is true in the bare bones format of Windows Movie Maker, where you can still alter the fundamental appearance and flow of your digital video clips. Here you can affect the speed, especially when you want to slow down a clip or sequence of clips in your Windows Movie Maker project.
Go ahead and find the clip, or clips, in your Windows Movie Maker project that you want to slow down go ahead and place them in the Timeline. You are going to want to use the Timeline view in this instead of the Storyboard view. Right click the clip and select Video Effects from the pop up menu. The Video Effects menu will come up with the available video effects in the left hand column and those on the selected clip in the right hand column. Go down in the left hand column and find Slow Down, Half, which will be under Sepia Tone and above Smudge Stick. Go ahead and select Slow Down, Half and then hit the Add button in the middle to bring it over to the right hand column. Once Slow Down, Half is in the right hand column hit OK at the bottom of the Video Effects window and it will be added to your Windows Movie Maker video clip.
Slow Down, Half dramatically affects the video clip you apply it to. It is going to bring it to half speed, doubling its length in the Timeline. This will also affect the sound associated with clip, making it deeper and more drawn out. It is best to use Slow Down, Half only when the clip does not have voice sound associated with it. You can use it for dramatic moments where a quick action occurs that needs to be focused on. You want to use this sparingly as it is so serious to the audience and over use will lose all of its emphasis. Try to use this only for one clip at a time, especially since Windows Movie Maker will not let you change the degree to which the clip is slowed down.