You are trying to view a website? In Internet Explorer? This MIME-type points at the Windows Media Player plugin, so you can play audio and video inside the browser. You won't find it here, because this forum is for XMPlay, a standalone audioplayer.
The plugin should be installed with Windows Media Player, you can get it from the Microsoft website. If you're using a different browser, the developers will have some info on plugins written down somewhere, either in the helpfile or on their own site.