All music and audio you wish to use in Windows Movie Maker must
be imported into the program.
To get music/audio: Click the Import Media button on the top menu. Locate the music/audio file you want to use and click Import.
Once the audio has been imported, drag it from the Imported Media pane into the Music/Audio track in the Time-line view.
Audio formats compatible with Windows Movie Maker include:
.aif, .aifc, .aiff, .asf, .au, .mp2, .mp3, .mpa, .snd, .wav, .wma