For those of you that are trying to get MP4 videos to playback on Windows Media Player you will need to download a MP4 codec from Microsoft. Look for filename WM9Codecs.exe on http://www.microsoft.com/downloads/details.aspx?familyid=06fcaab7-dcc9-466b-b0c4-04db144bb601&displaylang=en

This codec should get you playing MP4 videos within your WMP.