Well.
I'm running a genuine version of Windows XP with nearly none of the default settings changed since i installed, except all critical and recommended windows updates, and WMP 11.0.somethingsomething. I also use WMP's built in media server to let my PS3 stream audio and video from this machine. I don't even have that mfpmp.exe thing running, yet I have no problems playing back any media types, and no problems with the streaming to my PS3 either. I guess I can't help much, except stating the obvious: Your WMP is broken, reinstall :D.

Oh btw, I use TVersity as my media server for the most of my stuff, as it can auto-transcode on the fly when my PS3 encounters media it can't play. I still got WMP's server running too though.