Using Ease In, either on video or for photo motion, in your Windows Movie Maker project will give you that slow zoom effect that is great for different theatrical moments. Since Windows Movie Maker does not give you the same kind of motion and video effect controls that other non-linear video editing software does you have to start with a base amount of zoom, but fortunately you do not have to start there. Windows Movie Maker includes a way to increase both the speed and degree of zoom you can apply to your video and still image clips.
Find the video or photo clip that you want to add the dramatic zoom to and put it into your Timeline. Once it is here you can just right click it and select Video Effects from the pop up right click menu. Here you are going to then find Ease In from the left hand video effects column, which is right above Ease Out and right below Brightness, Increase. Select Ease In and hit the Add button in the center more than once. Each additional Ease In effect that is added to the right hand column will multiply the degree of zoom one more time. You can add up to six degrees of Ease In, which is the maximum amount of video effects that are allowed on the single clip. Once you have the number you want just hit OK at the bottom of the Video Effects window and it will be applied to the clip.
You have to make sure that you actually want to have this much zoom on your Windows Movie Maker video clip. If the clip is not in high resolution you are going to get defocus once you get close. Also, and extremely quick zoom will be so dramatic that it will stand out. Try out each incarnation of Ease In one at a time until you find one that you want. This type of dramatic Ease In will only work for longer clips, especially since shorter clips already have enough motion to maintain them. Like with anything in video editing, make sure this extreme zoom actually serves a purpose.