Not sure about what you mean by "put another video in front of my own", but as for making a spotlight appear from nowhere, this can certainly be done with Windows Movie Maker. Just make sure your camera is locked off so it can't move. Then take a few seconds footage of the scene WITHOUT the spotlight in it. Then, without moving the camera, take some footage WITH the spotlight in it. Bring the clips into your the editor. Have the clip without the spot on the timeline before the one with the spot, and just push the clips together. They will overlap in a "blend zone". When you play this edit, the spotlight will magically fade in from nowhere.