well first, if i may say this, dont use the wmp 9, its crap lol, i liek the
windows media player classic, an anhanced wmp 6.4.
(
http://www.divx-digest.com/software/media_player_classic.html)
now to your problem, i think it could be an error with your ffdshow filter,
try to download a new version (
http://sourceforge.net/projects/ffdshow/) and
install that one or disable it by right-clicking on the video while playing,
then properties and there doubleclick on the ffdshow filter and turn of all
the checkboxes of the several codecs, like divx, xvid, mp43 and whatever
there is. or maybe turn them on....
the problem you describe comes up when the video and the audio stream arent
sync anymore and then suddenly there comes a new keyframe and the video goes
faster to get sync with the audio stream again...
so it seems like the wmp9 installed a bad filter...
hope i could help,
Michael