Any idea how to turn your PC into a TV?

I heard you can turn your PC into a TV... does anyone have an idea where to start with this? I don't know why I want to do this... but it might have something to do with watching reality TV while I work at night or read blogs at night. Or maybe it's just that I love my little office so much I don't want to have to leave. Sad? Yeah... I think so too.