Are you creating a website to display your slideshow? If so then the best place to ask this is in Dreamweaver forum.
If you are creating a slideshow for your computermonly then I don't think you can have music in the background. however, Premier Elements is another program (I don't use it so I don't know anything about it) which creates video and all that so it must have music facility in it. Not sure though if it can create slideshows. Only the avid users of that program can answer this; Not me!!