HDTV is coming, so if you've just bought yourself a non-HDTV you've wasted your money. Really. Don't buy a TV now, because HDTVs are too expensive, and you'll have to buy another TV or a set-top HDTV converter box in a couple years when NTSC television goes away. If you don't have cable now, you'll also need to buy an HDTV tuner if your new HDTV doesn't have one, which is highly likely.
Note: This page refers exclusively to TV standards of the United States, since the rest of the world's TV signals are different. The general information may be useful, however, and some of the links are recommended reading.
Color NTSC television signal debuted in the 1950s, and this was the last time the format of television signals were changed. Not that TV hasn't increased in quality over the years, digital tuners, PLL broadcasts and a variety of other technical changes have improved the quality of the signal itself over the years.
Now we have multi-channel closed captions and signals to automatically set the time of the VCR all broadcast over the air. What hasn't changed is the amount of information a single channel can broadcast. Your audio and video TV signals are limited to a very skinny 6MHz of bandwidth, and right now we're squeezing every last drop of resolution out of it that we can.
HDTV was developed for watching movies at full quality at home. In the early 1980s high-definition video editing systems started appearing in production studios, initiating a push to move the systems into consumer's hands.
In the late 1980s and early 1990s, the industry worked out what the format of HDTV would be, and eventually decided upon a standard in the late 1990s. In the end, HDTV ended up with three new formats of television transmission, 480p, 720p, and 1080i.
These are the three levels of quality in the HDTV standard. The first is called Digital TV, or 480p, Enhanced Definition TV is 720p, and High-Definition TV is 1080i. The p is a progressive scan, where lines are filled in top to bottom, and the i is an interlaced scan, where the odd lines are filled in top to bottom, then the even lines are filled in.
These new resolutions give a clearer picture with more resolution, which allows for larger TVs. On regular television you'll notice the "pixels" of the image at about 7 times the TV's height. For HDTV this is reduced to 2.5 times the TV's height. (Yes, you are supposed to sit closer to an HDTV.)
The progressive scan makes it easier to present a clear picture on the TV, since interlaced TV signals can be difficult to combine properly on the TV screen.
I've hooked up my PS2 and Xbox to the television to run the lowest-end HDTV mode, 480p. There is a world of difference between the 480p and 480i in the clarity of the picture. Its well worth delaying the purchase of a new TV until you can buy an HDTV. You'll be kicking yourself otherwise.
Running DVDs in 480p gives a clear, clean picture. The picture is clear and sharp and gives you the feeling that you're back in the movie theater. The widecreen frame allows movies to be watch the way the director intended, eliminating pan-and-scan and allows you to see those details that happen off on the edges of the screen.
Note: Buy DVDs that say "Enhanced for widescreen TVs", "Widescreen edition" or "Enhanced for 16:9 TVs" on them. This way you won't have to suffer through a 4:3 signal when you get your new TV.
HDTV from the cable company costs an outrageous amount of money (digital package plus HDTV service plus equivalent movie channel package to get a single HDTV movie channel) and terrestrial (over the air) tuners are still prohibitively expensive to buy. Unless you really need to have the latest-and-greatest, now is not a good time to buy a new TV.
Most of the cheaper HDTVs are rear-projection models like the Toshiba 42H83 HDTV. Rear-projection TVs have problems with convergence which take fine-tuned adjustments with an onscreen guide and still don't line up 100% correctly. A TV with improper convergence leaves colors bleading across each other.
The other benefit of waiting is that all the nifty flat-panel TVs will and ultra-thin DLP TVs will drastically drop in price. They have better pictures and no convergence problems unlike projection TVs. Had I been buying a TV with my own money, I would have waited for the flat-panel or DLP TV to drop in price.