Well, I have 28.8Kbps...and, if it helps your analogy skills: You can stream a song to iTunes without having it rebuffer too much it as long as the bitrate of the song is less than your connection speed. In a theoretical world, that means that if you have a 24Kbps connection, and you connect to a station that streams at 24Kbps (the same as your connection speed), then you'll only need to buffer the first few seconds and never rebuffer.
Unfortunately, to listen to 128Kbps (example) streams w/o rebuffering, you need something faster then dial-up. There are other radio stations you can add to iTunes, but you need to do some searching on the Internet for them.