Apply the animations to autoshapes, then format the autoshape with a picture
fill. That way it's easy to change the pictures but not have to re-animate
them all. (This is Glen Millar's patented trick!)

Alternatively, use something like Animation Carbon http://www.mvps.org/skp/ 
or Edit (Animation Settins Painter) http://www.pptxtreme.com/ to apply the
animations.

You can batch import photos in a variety of ways:

BATCH IMPORT images into PowerPoint
http://www.pptfaq.com/FAQ00050.htm

In fact, using PPT 2003's photo album as described there will import your
images as autoshape picture fills, but because you have so many, you'd need
to apply the animations to each one, so it's not a complete solution.