PCHDTV.com has a $170 HD-3000 PCI high definition television tuner card for your PC. It supports HDTV over-the-air broadcasts, some HD cable, and standard television as well. NewsForge has a review, so it’s from a Linux perspective:

Standard television reception worked well in every OS I tested, but it was sort of grainy compared to other NTSC tuners. With some minor tuning I had Xawtv and TVtime working fine on my Kanotix install. VLC worked in every situation and ChrisTV worked fine in Windows XP. But of course, I could have gotten equivalent results with a much less expensive standard TV tuner card.

High definition, or ATSC, signal reception was a completely different story. I still haven’t been able to use the software that came with the product with my OS of choice, Kanotix, and there’s even less hope for XP. KnoppMyth worked, but my indoor amplified antenna was not strong enough to get any signal at all. After consulting AntennaWeb.org I bought an outdoor directional antenna with a pre-amp, which I believed would allow me to view HD television with my KnoppMyth setup. But I still had no luck; apparently, the low elevation and the dense forest in the area where I live effectively block the HD signal from the distant broadcasters.

NewsForge - Review: HD-3000 HDTV tuner card