My old team has just released Windows Movie Maker 2.6 for Vista. If you're running Vista on a machine that doesn't have a video card that is capable of running the new GPU pipeline that MovieMaker uses on Vista, then all is not lost. You can now install Windows Movie Maker 2.6 and you'll be able to run a version of MovieMaker that doesn't use the GPU for the video effects.

Windows Movie Maker 2.6