Here is the way

All you need is an SDcard the bigger the better
a SD card reader to transfer your files on your pc to the SD card

and all you need is this software
http://www.redkawa.com/blog/post.php?t=796

it will convert all video files and make it Compatible for your Wii

this is very impractical though because you can't save any of the movie files onto the wii
though you can post pictures of the video you are playing...

anyways it works it's a good converter and it will help you convert the files you want onto the Wii so you can watch movies and TVshows or whatever "yes even pron" if so you wish on the Wii through your SD card