I would like to add a little more to this thread if I may to answer the question.
A converter box will convert the HD program to be viewable on the older conventional TV set. And it will probably be a better picture than you have ever seen on your TV set. Even though it is not in High Definition it is still digital. Since a High Definition picture is wide screen. It should appear on the conventional analog TV set with a black bar at the top and bottom of the screen. What it is doing is reducing the height of the picture so that you can view the entire width of the picture without putting things on the picture out of proportion.
Wide screen TV sets have been around for a while. If you have one that is not digital the converter box will show the HD program at full picture size on the wide screen set. It will be standard definition and not high definition. It will still be the best picture that you have seen on your set.
If you have any questions then please ask. Most all of the normal stuff is on this forum. Ask if you cannot find it.
This forum has information in several places about converter boxes so I will not repeat any of that unless you ask.
In selecting a converter box I would suggest that you look for a box that will allow you to change the picture shape and size without having to dig through a menu to accomplish this. Most converter box remote controls have a button on them that will allow you to easily do this. The button may be labeled as zoom, picture, pixshape, aspect and other names that I have not seen on one of them yet.
There are and will be a few variations of picture size and shapes that is broadcast. A high definition TV will normally automatically adjust the picture for the best viewing on your screen. A converter box may not do quite as good of a job of changing picture shape and size for you. If you have a box or an HDTV that has this button on the remote then you can instantly change the picture shape to suit yourself.
Going along with sparks and if you're television is capable of viewing hdtv...The main item is making sure if your TV is built to handle High Definition signals (even if it isn't equipped with a digital tuner). Some TVs can display High Definition programming but do not contain a digital tuner, so in some cases, an HD Ready TV, may still need a converter box.
You have to be a little careful in the type of converter box you select if you're looking for High Definition. Some dtv boxes only output 480i for screen resolution, which is short of the normal high definition display resolutions that HD televisions can display (Current HD resolutions are: 480P, 720P, 1080i, 1080P).
Let us know what type of TV you have, and we can do a quick search and tell you if your TV is HD capable, or HD Ready.