Add following repository to your /etc/apt/sources.list
deb
ftp://ftp.nerim.net/debian-marillat/ unstable main
# apt-get update
Then
# apt-get install mplayer
or
# apt-get install mplayer-586
or
# apt-get install mplayer-k6
you'll probably also need codecs :
# apt-get install w32codecs