Vista Beta 2 still requires an NTSC tuner to use ATSC. The final product will not require an analog tuner for ATSC, so you will be able to use Media Center as an ATSC-only PVR if you choose. A separate NTSC tuner will not be needed for Cable Card receivers either.Why is this important? In the MCE2005, ATSC (over-the-air HDTV) required a NTSC tv tuner to be present so that the HDTV EPG data could be merged into your existing guide (i.e. the NTSC tv source). The design decisions and other history of geting ATSC support added to MCE are described by Peter Rosser in his blog entry titled "A Brief History of ATSC in Media Center".
There are currently workarounds to avoid this NTSC tuner requirement; however, they are hacks that aren't supported by Microsoft. With Vista, there will finally be a supported method to go with all digital tuners (i.e. no need to include analog tuners).