a volume slider is very easy to make IF you start with the
"right" movieclips: first create a movieclip called vcMC (volume
control movieclip) and place on its stage a slider track (called
trackMC which has one of its ends at its stage-center) and place
one the ends of trackMC on vcMC's stage-center. it can be any
length that suits your project.
then create another movieclip (called sliderMC that has one
of its ends at its stage-center) and place this movieclip in a
layer above the layer containing trackMC.
post a link to that fla and i'll add the code that will
control your sound objects volume.