You don't say what version of Mpeg you are working with. I suspect though
that you either have a self made Mpeg that does not meet the Mpeg standard,
or it is in a format (codec) that can't be used by PowerPoint.
Does your video software allow you to adjust size, color depth, frames per
second, etc? If so read up a bit on Mpeg standards and convert the video to
an acceptable standard. Second if at all possible use a standard Windows
codec for compressing the video.
If your not familar with how to go about all of this you might want to look
at our newest PowerPoint add in that resolves multimedia issues in
PowerPoint.
Austin Myers
MS PowerPoint MVP Team
Solutions to Multimedia in PowerPoint
www.pfcmedia.com