When TV images are transmitted digitally, that simply, is digital TV. Any kind of high definition TV is going to be digital. HDTV has become the latest must have for TV aficionados, and the impetus for new regulations for TV manufacturers.
With HDTV, resolution jumps to 720 progressive scans or 1080 interlaced scans. Although the 1080 interlaced has more lines, the 720 is progressive and you'll see better motion viewing. Either way, you'll see a sharper and clearer picture on digital than on analog. Both resolutions in high definition are available wide screen.
If you intend on watching regular TV shows, rather than HD programs, you will still get a better quality picture. This is pointed up nicely when you play your DVD movies on a progressive scan DVD player...this matchup gives you the best quality home viewing.
The Federal Communications Commission (FCC) ruled that by July 1st of 2005 all 36 inch and above TV's must include a high definition or ATSC tuner. A year later all 25 inch or larger TV's must have ATSC built in, and by July 1st, 2007 pretty much all TV's that have a standard NTSC tuner must have an ATSC tuner built in. If you are a cable or satellite TV subscriber, you do not need an ATSC tuner, just an HDTV ready TV as you can get the necessary cable box for your high definition ready set from your service provider. So the higher cost of an ATSC TV is an unnecessary expense.
Note that this does not effect many plasma and front projection TVs as they do not have this tuner installed.
Some industry watchers also caution you to get an HDTV with a special high end connection. Either a Digital Visual Interface (DVI) with digital content protection or a high definition multimedia interface (HDMI) will allow you to continue getting the maximum number of signals regardless of industry entertainment providers' copyright actions.
So you want this enhanced viewing experience...what do you need? You need an image that is captured in high definition, transmitted without any optimization, decoding by either a built in or external decoder (found in cable boxes and satellite receivers) and a high definition TV with a similarly high resolution as the original image.