Well If you want it as a channel download this:
http://www.mediafire.com/?tmrmemwjitt
Put the contents of the ¨On SD¨ folder to the root of your SD card. Then start the homebrew channel and then wad manager. Select the default settings (IOS249 and SD Card). Find MPlayerAX-MPAX.wad and install it. Keep pressing home on the wiimote to go to the system menu. You should now have mplayer as a channel.