I agree that the problem gets worse with large files, but you need large files to zoom/pan without loosing resolution. That is, the smallest part of the photo that will be displayed fullscreen should have enough pixels to view good definition. Also, if the panning and/or zooming is rapid, the required bit-rate is very high. The question is how much data can the CD drive process in an uninterpretable stream? Is this the same for all hardware configurations/speed? Does this maximum change when the slideshow is run from the harddrive? Does it change the second time the exe is played? I think what you're saying is that if it doesn't work, the file must be too big. I'm saying there's no maximum file size except the limitations of your hardware.