First of all, thanks for the fast reply!
To be more specific, I would like to build a Media Center that would allow me to see AVI videos, DVDs, and TV in High Definition (720p at least). I am not concerned about the capture card for now, as I live in Brazil and the digital standard for TV is quite different.
As you said there are other simple solutions for a standalone MediaCenter, could you please specify?
What if I wanted a Media Center with MediaDirectors around the house, would there be any mini ITX mobo able to do that?