Question regarding blockiness at outer fringe of video frame

Here's another question that came up, different project...

I am seeing what appears to be flickering square blocks which are appearing randomly in a single column or row at the outer edge of a Windows Media file as it is played in PowerPoint. The video file plays fine by itself when viewed in Windows Media Player. It's just when it runs within a PowerPoint presentation that we see this problem. 2 files have the issue-- one gets the problem on the outer right edge, and the other shows it at the bottom of the screen. Both files are approximately 856x480. PowerPoint is 2003 version.

By the way, the presentation works fine on other computers running PowerPoint2003. Info about the files shows the data rate running about 988 kbps... seems a bit too high... We're wondering if it's just too high a bitrate for the particular computer having the problem, or perhaps a graphics card issue...?

Thanks!

-Mike