I set it to automatically advance, then set the transition time to 1 minute.  
Still didn't help, as we don't want the slide to advance automatically, but
on a mouse click.  When I set it the way you advised, the narration starts
over on the next slide, which we don't want.  What the heck am I doing wrong?
Basically, here's what we want: 1) Start narration w/slide #1; 2) Click to
advance to slide #2, where 2nd narration sound will play; 3) Click to advance
to slide #3, where narrations 3 & 4 will play; 4) Click to advance to slide
#4, where we don't want any narration.  This thing gets so confusing!  Would
it be easier to just delete the sounds, then replace them and set them to
start automatically (like we just recorded it)?  Thanks for your help.