McGrath, I'm no expert on American BBC programming, but it started out being carried on our PBS (the only American network similar to the beeb, with no commercials). I'm guessing it works like any other programming on that network, ie the local affiliates have some choice in the matter as to what they carry. However, they have expanded, and now have a cable network. Their website is here:

http://www.bbcamerica.com/bbcamerica.jsp

The BBC programming on PBS is all I have access to, and it is pretty high quality, if somewhat dull. The cable channel is like any other cable channel, really. With the exception of news coverage being a different bias from the ones we're used to in the US.