Did you know this? In order to setup the WMCE part of Vista, it requires you to have a NTSC tuner card. An ATSC, or digital, will not work. It is a requirement by Microsoft to have an analog tuner card in your Vista box to watch digital TV. Sure, Vista is still in beta testing and all, but do you think that the Vista team knows that the NTSC tuner will be shutoff on Feb. 17, 2009. This is the same case in the Windows Media Center 2005 but it should not be in Microsoft's latest and greatest OS. There is a workaround however, even though you shouldn't have to use it. A person could use an external USB analog tuner to setup Media Center then use whatever tuner they want.
UPDATE 1: Fixed digital switch-over date.