Depends. Yes, you should use a TV Tuner like Bobo says. However, a VIVO graphics card should be able to as well. You would just have to run the TV signal into something like a VCR or DVD player that can output in a different format. From there you could output in Svideo, composite, or whatever your graphics card supports and the VCR/DVD player can output with - into your VIVO-capable graphics card.
If your graphics card doesn't have VIVO, then the plug on the back is output only. By plug, I mean whatever is on the backplate besides the VGA and DVI connectors.