Hopefully, I'll be able to fill a very frustrating void that I've encountered. Many sites claim that streaming video to your Wii over a local area network is easy as pie, but I have yet to see detailed instructions. So, here you go!
Step 1: What you'll need:
The Homebrew Channel.
MPlayerWii, loaded properly onto your SD card.
On your computer, you'll need to install VLC, a small but full-featured media player.
You'll also need to find the local IP address of the computer(s) you want to stream from.
To do this, open a command prompt and type "ipconfig." This gives you your IP address. Write it down!
Now, open the "mplayerwii.conf" file on the SD drive, and add a line that looks like this:
"stream = http://[your ip address]:8080/"
So, my line would look like this:
"stream = http://192.168.2.2:8080/"
Save that file, put the SD card into your Wii, and load MPlayer from the Homebrew Channel.