I do a lot of ppt presentations with video clips. Not only do i do the training but i also create clips for my department of trainers. I will admit,I have never used HD clips in my ppt, but I do know that I have had more success with WMV files (the Microsoft codec for video), than with mpg or any other files. PPT has been very tempermental for me, and sometimes mpgs, if they are small files, will work. But, agaiian, WMV files have worked best for me. Perhaps others may be able to shed more light on the issue.