|You might need to download an audio extraction tool. If you can get the audio into a separate file (mp3, wav, etc.) you can add it to the Movie Maker timeline, on the audio track. Be aware that you'll have to manually sync it up with the video.|
A google search (e.g. extract audio from video) should produce a number of freeware programs (audio rippers/extractors) that'll do the job.
My guess is that the video uses an audio codec that is incompatible with Movie Maker.
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