I think Microsoft is unable or unwilling to supply some of the codecs you need. (e.g. Divx 5 or xvid) There are other places on the net to download them once you have identified them.
To identify the codec required, download the free tool "GSpot", which will report what video and audio codecs are used for the movie file.
Then use Google to search for the names of these codecs and find a download site. Download and install the codec manually.
Next time you play the movie, WMP should magically find the new codec and play the file correctly.
All of this has worked for me with WMP 8 and 9. I've never tried 10, but provided that Micro$oft hasn't crippled it too badly with DRM, it should still work.


