|"I thought that all Cards in Computers were digital? Aren't they?"|
That's not what wizard-fred is referring to. Fred was asking you whether or not your TV capture card has a digital tuner (ATSC) built in. I can't find any information on the card you listed, so I do not know whether it's a digital or analog. Chances are, it is an analog tuner built into your TV card. If that's the case, you won't be able to watch HDTV on your computer.
Analog Tuner = Noisy picture reception. Stereo sound on network channels, mono on cable ones. Has been phased out here in the U.S. 480i resolution.
Digital Tuner = crystal clear reception, digital 5.1 sound, 480i, 480p resolutions.
HDTV Tuner = crystal clear reception, digital 5.1 sound, 480i, 480p, 720p, 1080i resolutions--some may support 1080p, I'll have to check on that. However, few stations broadcast in 1080p, perhaps only some premium movie channels.