A few notes: The converter boxes have been on the market since last March. They were intended to be sold primarily between that time and this past February, after which there was little reason to think that there would be much demand for them. In addition, a lot of folks bought converter boxes that didn't need them, just to take advantage of the CECB coupons that were made available. As a result, many retailers are running out of converter boxes, and manufacturers don't see enough demand remaining to warrant another production run. So it may take a little bit of work, depending on where you live, to track converter boxes down. If you're having trouble, check eBay. You cannot use CECB coupons that way, but at least you can get the device you need.
Next: You probably want to go to
http://tvfool.com, click on >> Start Here <<, enter your
full address, then click "Find Local Channels". This will give you an excellent view of what you can and cannot expect to receive with various antennas.
Note that it is really important (though not required) to enter your full address, because different parts of town might be higher or lower than others. That makes a big difference. I live in a low area, but on the southern side of a hilly ridge that runs through town. Folks on top of the ridge obviously will get somewhat better reception, but folks just over the other side of the ridge, still in town, get much worse reception (you'll see this described as "1edge" or "2edge").
Generally, with any decent indoor antenna you should get good reception for any station shown in green, but only as long as the antenna has a relatively unimpeded view of the direction where the station's transmission towers are. (This is also indicated on the graphs available from tvfool.com.) Stations in yellow are problematic with indoor antennas -- sometimes you're okay, sometimes you're not. And unlike with analog television, there is no significant in-between. Digital reception is like a cliff... either you can get reception or you cannot.
Stations in red, or with a "C" indicating a co-channel conflict, you probably will have a lot of problems receiving, except with an excellent outdoor antenna. The "C" stations may only be available to you if you have a directional antenna.
I'd be more than happy to help further, if you need it. You can post your zip code (for somewhat accurate insights) or PM your street address (leave off the house number; I don't need that, unless your street is excessively long).
Or, if you prefer, there is a website forum devoted to helping folks figure out what they need to do to get over-the-air reception (though they'll need the same info):
http://www.dtvusaforum.com