Help with iPhoto '08 - Slideshow & Ken Burns

I need help with creating a slideshow using Ken Burns effects. The basic problem is that some photos are getting cut off. I know I can modify each photo for start/end place, but each time I run the show, the effects are different (one run, slide 1 goes left to right, next run it zooms out, etc.), so I can't tell which photos need to be individually modified. The show is 100+ photos, so I'd rather not modify each one. I was at the Genius Bar yesterday and the guy told me the effect would be consistent once I made the slideshow, so that I could tell which ones to fix manually, but that's not the case. Please help!!

Running: MacBook OS X 10.6.8, iPhoto 7.1.5

Thanks!