You would have to "stitch" together several pieces of music into a single
file and then use this file. Plenty of software to do this just by searching
on google.
Also, you can add your photos in Photo Story Plus. Then open the file with
Windows Movie Maker (part of XP under Accessories and Entertainment) and add
the music there since it will let you add separate tracts.
However, this last option is a little more complicated and if you want to
try this you may do better by simply opening Movie Maker and importing your
still photos in it and then adding as many pieces of music as you want.

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The only way I have found to add multiple sound
files to a PhotoStory is to combine the files into
one. There is some info on how to do it at the
following site:

Photo Story 2 - www.photostory.papajohn.org
(Wait for the left column to load and go to...
Setup Music)

You can sign up for a free newsletter about
PhotoStory and MovieMaker on the "What's
New" page of the following site:
Movie Maker 2 - www.papajohn.org