try using media player 10.. coz if there will be missing codecs or something, it would prompt you.. and have you choose to go to web help to download missing codecs if its available...
I had this when I got my replacement graphics card a few weeks ago (had SP2 for ages)... I fixed it in the display properties (under "settings" -> "advanded" -> "options") by un-ticking the box for "WMV acceleration".
Maybe its since i installed wmp 10?That might be it. I turned off that option but it still happends. Is there a way to unupdate windows media player and have it not auto make me update like it did last time?