(get it here: Zoom Player)
But I just found this neat little program:
VLC Media Player
It's a crossplatform (!) media player and streaming server. Best of all it plays nearly every codec you could imagine, so no need to download all those codecs anymore. plus, you can set slowmotion to 0.5, 0.25, down to 0.13
and it is highly configurable, too
One more thing; I've had quite a lot of movies that played too slow on my computer (560Mhz P3)...VLC Player plays them all perfectly.
Enough recommendations for now..laters.
(I hope, from now on, nobody will use the ultra-crappy Windows Media Player anymore...)