Please visit the links for more info, but the Guncon2 is the Playstation 2 gun made by Namco.
It is USB, which is why it can be used with PC (with Smog's driver). It can be used on a TV (assuming you have a TV-Out card with composite out) with no modifications as it was intended for TVs. It can be used on arcade monitors by constructing a small conversion circuit (see Smog's Blog).
It cannot be used on PC monitors or Projection TVs (unless you happen to have a model that you can already use the Guncon with for PS2, there supposedly are a few old ones that work)