You can always find this info on the MIME type list at mozdev.org: plugindoc.mozdev.org
In this case it's Windows media. So if you haven't already done so, you will need to add the PLF repos to your software sources using easy-urpmi, the link is at the top-right of the forum page. After you have added the PLF and updated your media sources, you will need to install (from the PLF repos) the mplayer, and the win32-codecs packages. Then install the mplayerplugin package from the Mandriva repos. I would also suggest installing the real-codecs package why you're doing this.
Let us know if that works for you, and welcome aboard! :)