Did you check the physical dimensions of the inserted image? It may be that some re-scaling is occuring during the transfer process and the image is being distorted as a result. The dpi is irrelevant here; it's the pixel counts that matter for the nominal aspect ratio. If the physical dimensions of the inserted image retain the 4:3 aspect ratio you require, the issue may be with PowerPoint itself.

__________________
Cheers,
Paul Edstein
[Fmr MS MVP - Word]