screensaver problem

I recently bought a MacBook Pro to replace a badly performing old Dell Laptop. I am interested in running a "My Documents" screensaver using the same pictures that ran on the laptop. These pictures are on a DELL desktop in another room of the house running Win XP SP2. We are hardwired with Cat 5e ethernet and are running a standard LAN.

The pictures do come up (although much prettier on the new screen!), however, about one in ten will display rotated to the right 90 degrees. I was sure that this was because some of my pictures were not correctly rotated, but I proved that not to be the case. It doesn't seem to matter if I instruct the System Preferences to center, zoom, or crop the pictures.

Any ideas?

Go into preview and rotate them 90 degrees the opposite way and save
them like that. It might show up wrong in my documents but
right on the screensaver.

The thing is, only about 10% of the time are the pictures displaying sideways. There's something happening between the MacBook and the DELL desktop that I don't fully understand.

If I rotated all of my pictures (about 8000), then 90% would be sideways and only 10% would be correct.