Bingo, Kris.
I should have looked myself, but I just began to think about the possibility of "compression" yesterday afternoon. She's still working with only '06, I think, but I have '09 coming in the mail in a day or so.
In any event, some of her own exploring, I learned late last evening, produced the info that the "slowness" and "choppiness" may have arisen from the kind of iTunes files she was attempting to use. One of Apple's forums gave her a workaround (since I've never done any of this even once myself, I don't quite grasp it) and so now she says everything working OK.
It's curious, since some of that music she also used in earlier DVDs, without incident. So, she's happy and Grandpa is happy. Thanks to everyone.
When I understand what the key elements are in the workaround I'll post them here, in case they are useful to others.
2008 was a busy year for her family, so this 80 gig movie is a big (emphasize BIG) production and she is quite invested in its success.
When I think of (look at) the pics (inclusing Polaroids!) we took of her childhood 40-45 years ago, while most are quite enjoyable, they are a far, far cry from the beauty of her iMovies, including sound track.
They don't make 'em like they used to!