Have you registered yet? I'll assume you have. Have you tried playing one of the concerts? What happened?
Over dial-up, it will take longer to actually connect with the stream itself, but you might be able to do it. Be patient and just see what happens. Once the stream starts coming thru, it's just a question of whether or not it will play correctly without interruption caused by buffering or whatever. As far as I can see there is no link to actually download these concerts to your machine, but that would take too long over dial-up anyway, so don't worry about it.
Ftr, I've been able to listen to other streaming media over dial up; it played fine.