buy a dvb, and easy cap video capture. less3 than 50$
I think the artifact you're looking for is a "video capture card", although it doesn't have to be a literal card. They make ones you can plug into a USB port. E.g.http://www.newegg.com/Product/ProductList.aspx?Submit=ENE&IsNodeId=1&Description=usb%20video%20capture%20device&bop=And&Order=PRICE&PageSize=20
That is not the right question to ask. The question to ask, however, is how can you get the tv antenna into your computer, and that is accomplished with a tuner card.