After having successfully hacked a Wii a couple weeks ago, I managed to get wireless video streaming working as well last night. I was able to stream just about every movie file format (with the exception of a DVD .iso file) from a Vista PC to the Wii over wifi. The app I used was MPlayer CE, available via the Homebrew Channel. Not too shabby. Mplayer supports Windows shares, which makes life easy. Video quality was adequate. It would be improved significantly if we were using the Wii component cables. For those looking for a way to view downloaded movies and TV on your Wii from a PC, this is currently the best way that I've seen. There are other media streamers that work with the Wii, like Orb, but they require transcoding to Flash, which degrades video quality significantly and takes extra CPU cycles.
for the first time. By that, I mean I installed the 
unlocked the full potential of the Wii. The Homebrew Channel has downloadable utilities, homebrew games, emulators, media players, and every other doodad that you wished the Wii legitimately had. It couldn't be easier to use. If you have a Wii, I highly suggest you consider modding it like this. I was so impressed that I might actually have to buy a Wii myself.