It will depend on how the music was put into the slideshow and what format was used. Here is a method you can try.
1. Open your pps file in PowerPoint
2. Click on File, Save as HTML or Save as Web Page depending on your version
3. Follow the steps to convert the presentation to HTML in a new folder
4. Locate the folder you created for the files to be saved in. Look for files ending in .wav or .mp3 or other types of audio files. They may vary depending on the type of audio files imported into the presentation.