You're probably much better off to use WiiMC (native Wii homebrew app, decent media player, but not quite of the same calibre as XBMC) or possibly GeeXbox (a specialised Linux distro for media usage). I haven't tried GeeXbox, but I use WiiMC reasonably regularly and it's certainly pretty decent. Doesn't have the impressive metadata features of XBMC though (stuff like cover art etc. for movies & TV shows).