Bentley,
When you're making your presentation, click on view at the top of your
powerpoint window, then choose "Master" and within master choose "slide
master". Now, anything you insert in this view will automatically be on every
slide in your presentation.
If you want a piece of music or a recording to keep playing, continuing from
slide to slide without re-starting every time, then insert it on the first
slide in the normal view. Then click "slide show" at the top and click
"custom annimation". You will see the song or sound you inserted in the
custom animation window you just opened. Left click on it and choose "Effect
Options...". Under "stop playing" choose "after" and then type in the number
of slides you want the sound/song to play for.