If my car died tomorrow, I'd have a lot less angst picking its successor than I would if my TV conked out. The "digital transition," as it's called, has given the television market some of the same frustrating inscrutability as the computing market, with an extra dose of technological, regulatory and economic uncertainty.

And yet: People are buying these things. Not just the techno-victims who will snap up any unproven gadget with a four-figure price tag, but regular folks who simply want a better set when their old one implodes.

Finding that better set without buying more or less than you actually want is the real trick of the digital-TV market. Here are six riddles to keep in mind:

Digital and high-definition TV aren't the same thing, except when they are. HD is a subset of digital TV, a generic term that covers 18 possible combinations of picture resolution, screen proportions, scan mode and frame rate. Only six of them count as HDTV -- only two of which broadcasters actually use.

(Why 18 digital-TV formats if so few are used? Much of the consumer-electronics industry remains stuck at a kindergarten-playground level of conflict resolution; when the Federal Communications Commission had to pick a standard in the mid-1990s, embracing all 18 formats available was the best it could do.)

One of the two HD formats is called 720p to indicate its 720 progressively scanned lines of resolution; "progressive" means that the entire image on the screen is refreshed 60 times a second, the way a computer monitor works. The other is 1080i, for 1,080 interlaced scan lines; in this case, half of these lines are refreshed every 60th of a second, the way old-fashioned analog TV works. Both 720p and 1080i are wide-screen formats, with a 16:9 aspect ratio close to a movie-theater screen's proportions.

Vendors, however, often try to fudge whether a set is HD-capable in ads. Pay attention to an HD set's resolution -- except when it doesn't matter.

Many digital sets -- including some large, pricey plasma screens -- only support a third, lower-resolution format called 480p (short for 480 progressive scan lines). This format, still a big step up from analog TV (which uses 480 interlaced scan lines), is often marketed as "Enhanced Definition." But on those 42-inch plasmas, the difference between ED and HD won't be hard to spot. When in doubt, look up a set's resolution in pixels; if its vertical resolution (the second number listed in a figure like "640 x 480") is below 720, it's not HD.

Conversely, on smaller sets -- say, under 25 inches across -- it is difficult to see the difference between 480p and 72op or 1080i from normal viewing distances. On those televisions, you can get away with enhanced definition, saving yourself a few bucks.

Like analog TV, digital TV broadcasts can be received in a variety of ways -- over the air, or, for a much larger selection of channels, over cable or via satellite. But digital cable or digital satellite isn't the same thing as digital TV. The services that cable and satellite providers have sold for years are analog at heart; they're only "digital" in the way they transmit that conventional signal. Real, HD-capable digital TV via cable or satellite costs more than "digital" cable or satellite and brings a smaller selection; many cable channels haven't brought out HD versions, although this is quickly improving.

Then there's over-the-air reception, something that seems an anachronism but need not be with improving digital receivers. If you get an acceptable analog signal, you can get a terrific digital signal, as our latest tests have found. But while any analog TV sold today only needs an antenna to tune into what's on, most digital sets are missing any digital tuning hardware.

A set sold as "HD-ready" isn't ready for HD. That phrase, "HD-ready," really means that the set can display an HD picture if it's fed a digital signal by an external box -- a cable, satellite or off-air tuner. A small but growing number of TVs called integrated sets now include an over-the-air tuner, often called an "ATSC" tuner after the Advanced Television Systems Committee that devised the digital system.

A smaller number of sets can tune in to digital and HD cable signals without needing an external cable box. Those with a "QAM" tuner can get unscrambled digital cable, but not premium fare such as HBO; this is the functional equivalent of a "cable-ready" analog set. Those with a "CableCard" slot can get a full set of channels if you pop in a small ID card provided by your cable company, but it won't allow any interactive cable services, such as video-on-demand.

An HD set that included a satellite tuner might be a good idea, but it doesn't exist. Sorry.

Many of the technologies I've mentioned here are new; CableCard sets, for instance, went on the market only at the beginning of last month. So it still pays to hold off on an HDTV purchase if you can -- just not for too long. This is an issue of technology, economics and politics: The technology keeps getting better and the prices keep getting cheaper, but political considerations are forcing manufacturers to put in features that viewers probably won't appreciate.

Last year, the FCC unwisely voted to require that, as of July 1, 2005, any device capable of receiving a digital signal off the air must support the "broadcast flag." This scheme is supposed to stop full-quality copies of digital programs from circulating online. The idea is to boost the selection of HD shows available over the air and thus speed the digital transition (the government needs stations to switch to the new digital frequencies they've been given for free so it can, in turn, auction off part of the old analog spectrum).

I doubt that the broadcast flag will stop Internet copying of programs -- people will just share lower-quality copies of programs that take less time to download -- but I am pretty confident that the flag will do a fine job of inconveniencing law-abiding viewers. You would be wise to buy an HDTV, or least an off-air tuner, before the FCC's deadline, assuming its manufacturer hasn't implemented broadcast-flag support ahead of time (as if customers are screaming for this feature today).

If you buy too late, or you buy a set that's already flagged, there's still a way out of this copy-restriction mess. Make sure digital-TV hardware has analog connections. Analog component-video inputs and outputs offer almost the same quality as digital connections, but they can't enforce the copying limits of the broadcast flag or its equivalents in cable and satellite transmissions. Make sure that your digital tuner, however it gets its signal, can send the picture along to a TV or a video recorder via a high-resolution analog output.

Digital television has spent most of the past decade as a moving target, and that's not likely to change for the next few years. But I think -- or maybe I just hope -- that if you keep those principles in mind, you can find a digital set that has the useful lifespan of a TV as you've known it, not that of a computer. It's been wonderful to see such rapid progress, but at a certain point, digital TV has to become as boring as analog.

Living with technology, or trying to? E-mail Rob Pegoraro at rob@twp.com.