Long Answer: You CAN, but due to the limitations of the Wii hardware & the Internet Channel, you’ll need to use some software on a computer connected to your network to do so. You’ll need a fast computer with a lot of RAM as it’ll have to do the grunt work on converting the video streams into something that the Wii & the Internet Channel can handle.

All you do is pick up the Orb Media Player ( http://www.orb.com ) & install it on your computer. Please be aware that you’ll need at least a 2.4 Ghz processor, a broadband connection & a computer that’s capable of handling Windows Vista or 7 (as they have similar RAM requirements) for maximum enjoyment, specially for streaming video.

Once you have Orb installed on your computer, you just log into Orb’s MyCast website to access your media & streams from your computer.

I will note that if you have Winamp installed on your computer, you can just pick up Winamp Remote (which is powered by Orb) to do this as well.

Please be aware that video quality will most likely be less than desired on the Wii due to it’s hardware limitations, but it’s possible.

Hope this helps!
References :