I haven't loaded any codec packages that didn't come with Windows and I haven't found anything that Media Player won't play.
I think that the .mov codec may have been installed by some software I installed like Adobe Premiere but I'm not sure.
But I can run AVI, MOV, Mpg, WMV, DVD, I can't really remember anything I've tried to run that didn't.
And I use it for everything. I don't have any other player except for QuickTime which I try and avoid.
I too know, it's an older thread, but never to old a matter to be discussed. I would agree with Mike Hawthorne above, having run ffdshow, K-Lite, and a few others, I've sort of gone back to the basics, running Windows as far as it goes. Although having lost my MediaPlayer for some reason, VLC works fine with basic Windows codecs.
The main thing is, not to have several codec packs. They just war each other!