Open your Window's system.ini file with a text editor like notepad (not wordpad or word). Find the line "MPEGVideo=mpeg16.dll" (probably under the header "mci") and change it to "MPEGVideo=mciqtz.drv". After making the change, save it as system.ini and do a Restart of your system. Return to PowerPoint or the Viewer and try running the presentation again.

That should do the trick. Let us know if you still have a problem.