Depending on the equipment you have there are a couple ways you could
achieve this.
The easiest way would be just plug in a microphone to your soundcard and
choose narrate timeline from Movie Maker and start naration while your tape
is playing back from a stereo loud enough for the microphone to pick it up.
Doing it this way will of course give you poor audio quality.
Another way would be to use the low-level audio output of a stereo tape
decks RCA plugs and run those to your line in on your PC sound card using a
RCA to mini-din type connection. Then you can choose narrate timeline from
Movie maker choose the line-in as your source and press play on the tape
deck. This would give you much better quality.
