RivaTV

The RivaTV project "aims to provide driver support for nVidia based graphics cards with video-in feature and some of the video capture chips that come on such cards. The driver also activates tuner and audio support provided by the V4L project." Note, however, that the site provides a clear warning that it does not offer support for a number of personal cinema cards (with the 7174HL chipset).
The list of supported cards is here.