In the last part of this special series on high-definition TV, Katy Sai looks at the pros and cons of various HDTV sets from tube to plasma.

MADISON, Wis. -- It seems everywhere you look you're told why you should buy a high-definition TV, but when you actually go to the store, it's confusing.

"They know they want it. They know the picture is very pretty, but they don't truly understand how to get it and what their choices are," said Dave Shepard, senior vice president of marketing at American TV and Appliance.

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There are so many choices. One of the most noticeable differences is the shape of the screen. Most high-definition sets have a wide screen while conventional sets are nearly square.

But the shape of the screen isn't what's critical for high definition. It's what's behind the screen that matters.

Several different technologies can produce a high definition image. The traditional TV most of us have at home uses a tube to produce a picture.

A newer technology is LCD, liquid crystal display, which is used on many computer monitors. Comparable to that is DLP, digital light processing, in which a tiny chip produces the image.

"It looks like a mirror, but it's much more than a mirror," Shepard said. "It's actually 1.2 million mirrors on this small chip."

An advantage to LCD and DLP is that the screens won't burn an image. Plus it's lighter.

"A TV that was traditionally built would weigh several hundred pounds," Shepard said. "This is less than 100. Additionally, it's very narrow, only 18-inches deep as contrasted with a traditional TV, which would probably be 3-feet deep."

Even lighter and thinner are the plasma TVs, which are far more expensive.

"Here we don't have a picture," Shepard said. "We have, instead, 1 million tiny neon lights. They're filled with gas, that turn on and off when the electronic circuitry in the television set tells them to."

Consumers often interchange the terms "plasma" and "high definition," but "about half the plasma TVs on the lower end of the price spectrum are actually not high definition," Shepard said.

That's where it gets really confusing. Any of these new technologies can be, but aren't necessarily high definition.

"It's possible to have a digital television that's not HD, and it would be unfortunate for a consumer to make an uninformed choice and then later be disappointed," Shepard said.

To get a true-high definition image, make sure the set you are buying either has a built-in tuner or is "HD ready."

"HDTV-ready means that you have the display to watch HDTV, but you don't have the receiver to receive it," Shepard said.

That requires you do something in addition to purchasing the set -- either buy a receiver to get a high-definition signal or get a tuner that corresponds to a satellite or cable system.

With all these choices, the big question is: Which is best? Experts say only you have the answer. Is your priority a set that's lighter, thinner, bigger, cheaper? You need to decide what's most important for you.

Before you buy, do your homework on high-definition, so you'll be clear about how you want to make the jump to the next generation.

Eventually, you won't even be able to buy a standard analog TV, Sai reports. A federal court ruled this week that manufacturers must include a digital tuner in most new TVs by the year 2007.

After broadcasters switch to a digital signal, you'll still be able to use your standard TV at home if you add a digital tuner, but you won't see the pictures in high definition.