if you are making a linear presentation, then you will need to include the mp3 within the SWF and not load it as an external MP3.

I think your best solution is, as Frets recommends, make a video and burn it to CD. The overall file size will probably be smaller than having 400 separate photos and audio. Also, if there is no interaction then you wont really need Flash. All you need is video authoring software.