SusiQ,

Sorry I don't have PhotoStory, but the product description says it has three modes of operation -- overview, storyboard, and timeline. For multiple pictures you would need to be in timeline mode (a set of numbered tracks) where you can stack many objects to appear at the same time and then apply size and position effects to each individual image. The mode selection icons are the three at the very left of the editing window.

The sample slideshow has several multiple picture transitions.

Regards,

Carl