Install all ia32-libs packages
sudo apt-get install ia32-libs lib32asound2 lib32ncurses5 ia32-libs-sdl ia32-libs-gtk lib32stdc++6 ia32-libs-openoffice.org2.
Download the package
Install the package Using the following commands
sudo dpkg -i mplayer32_1.0pre7-1_amd64.deb
sudo dpkg -i mplayer32_20070130-1_amd64.deb
Fetch the Win32 codecs from http://www.people.virginia.edu/~drf8f/MPlayer/releases/codecs/essential-20060501.tar.bz2
Unpack it and install to /usr/lib/win32.
tar -jxvf essential-20060501.tar.bz2
sudo mkdir /usr/lib/win32
sudo cp essential-20060501/* /usr/lib/win32/
Use mplayer32 to play wmv9 files (but it can also be used for other files as well )
If you want a 32 bit mencoder as well, you can download it from here
http://www.stud.ntnu.no/~grannas/debs/mencoder32 and put it into /usr/bin/ .
If you want to use the gmplayer gui, rather than the command-line do the following:
sudo rm /usr/bin/gmplayer
sudo ln -s /usr/bin/mplayer32 /usr/bin/gmplayer
This operation has to be done manually as the gmplayer file is "owned" by the original mplayer package.