Yes it can be done. You run the program Orb (http://orb.com) on your computer.
Well this Orb program, it installs on your computer, and you designated a folder for it to go into, and you put all your media you want to use on other devices in that folder. Then you make an account and attach your computer to that account. Then say you want to watch a show from your computer on your wii. You go on the internet channel on your wii and sign into MyCast on Orb (just google it) and you can get all your media on your wii.
Warning: I know all of the above information. The following information I am not sure about.
There is also some sort of card (I think it was a TV Tuner Card) and you put that in your computer or something and then you can use it to watch internet tv on the computer. Using this, ive heard you can watch that on the wii.
I've never tried this other than watch some family guy on the wii. Worked fine. Hope this helps