Microsoft Knowledge Base Article 316992 contains the following summary:
This article discusses the multimedia file types that Microsoft Windows Media Player supports and provides a sample of most of these file types. If problems occur when you play a supported file type from another source, Microsoft recommends that you try a sample file from this article that has the same extension. If you can play the sample file, there may be a problem with the file from the other source that you are trying to play. If problems still occur when you play files from this article, view the following Microsoft Web site for additional information to help you troubleshoot your problem:
http://support.microsoft.com/highlights/wmp.asp
