there are converters to make a wmv8 into xmv but to get xmv to any pc media there is not
(that i know of)
now on that subject there are converters to make a file named .bik (also movie file) work on pc
the bik to pc converter is in the tutorials section heres a link (http://www.xbox-scene.com/articles/intro-movies2.php) just read and you'll find where to download bink (RAD video tools)
as for which games have which type of movie media and why? i do not know you'll just have to get lucky.
hope this helps