Your current television will work as it does now until analog broadcasting stops. Even after the transition is over, your current TV will not become obsolete.  A converter box can be used to receive broadcast DTV signals and change them into the format of your current television.  In addition, if you use your analog set with a multichannel pay service like cable or satellite, it will continue to work as it always has.  Even with a converter box, however, your current analog television will not be capable of displaying the full picture quality of DTV.  To enjoy the full picture quality, you must have a DTV set. Subscribers to cable and DBS services should contact their providers regarding converter boxes for those services.

What do DTV sets look like and what will they cost?
Most DTV sets have wider, more rectangular screens than current analog TVs. This widescreen format allows for images that are more like those shown in a movie theater.  Like current TV sets, a range of sizes is available. As with most new consumer electronics technologies, DTV sets have become less expensive since their introduction.  Prices are expected to continue to decrease over time and will vary depending on screen size, display technology, and other features.

Source:  http://www.dtv.gov