Could you give more info? I wanted to do this before.
He's right in the sense that you can technically hook up your cable box to your monitor assuming your monitor and cable box both have HDMI ports.
Most cable boxes use HDMI and/or composite cables for high definition, and brown townog standard definition (Yellow/red/white cables) for non-high def.
Most old monitors will have only VGA. Most monitors have VGA, DVI or both. New monitors usually have HDMI, which are becoming more frequent for displaying graphics since most high end cards now have mini-HDMI output.
If you have an HDMI monitor and your cable box has an HDMI output, and you have the cable line in your room, then yes theoretically you can watch TV on your monitor.
It's more or less useful if you have a monitor that has both DVI and HDMI, so that you can have your PC on DVI and whatever else, console/cable box etc., on HDMI.
