You can edit audio/music in Windows Movie Maker. You can increase/decrease volume levels, mute, fade in/out, clip/split. These options are available by right-clicking on the Music/Audio track. The Video audio also offers similar editing features by clicking the + button beside the Video track.

Also, take a look at this site for more information:
http://www.funadvice.com/q/cut_off_the_beginning_of_a_song_using

I hope this helps!

Brett M,
Windows Outreach Team