Here is my suggestion being someone who has ran a recording studio. If you are using audacity what you need to do is make several audio files (Probably in OggVorbis Format) Each audio file should be for the each slide. This will allow you to set the timing exactly how you want it. Now there comes the issue with the music. This will need to either be a completely different file set up on your first slide with a setting to play through all slides or another trick you can do is use Audacity to fade it out for each audio file.

Now based off of your first post you may not know how to do all of these things. In order to find out because you are the one that gets to choose how you want to do this just google them. For example to make an audio file play for all slides you would google something like: PowerPoint 2007 play audio for all slides

This should give you a good starting point.

Let me know if you have any other questions.

Thanks