I have never used the program in my life, but my friend made me download it so I could watch some of his animations.
Then I found out you could save it as a .gif file.
http://img211.imageshack.us/img211/5227/pivotlp3.jpg
So ya you should be able to save your pivot files as .gif (animated gifs)
Then to convert these .gifs to a movie file you could probably use Windows movie maker to save it as a .wmv file or maybe even Super
SUPER © .
I'm not even sure if you can convert gif to like avi with Super, and I hate the program anyways, so ya. I tested with Windows movie maker and it seemed to have worked fine.
Just note I'm pretty sure youtube lets you upload .wmv, but I'm not sure cause I don't have a youtube account.
Hope that helps.