I was taking a look at this app: http://www.ztitch.com/index.html and was wondering how they did all of the 3D stuff... It doesn't look like he is using the built in 3D rotations (PlaneProjection) in Silverlight, but he must be doing something with 3D Matrix Projections...
What math is involved in this specifically? Is it true rotation or is the app just "skewing" the pictures into a trapezoid shape when they get closer to the edge of the screen to make it appear as if the images were in a sphere?
P.S. The main reason I think this isn't the built in 3D rotation is because there isn't any depth-fighting-- an image in the back is always in the back, regardless of what angle it's rotated at...
They do use Spherical Coordinate System for displaying images inside it.
Z-fighting can be configured through depth bias or image proportions (sphere size) (float should be enough for your task).
Also you can get some code here.