If your Internet radio can "tune in" to Twonky. I see no reason why any of the multitude of streaming media clients available on the Pandora can't either. You'll have a wide variety of choices available.
From what I remember twonky is a upnp server ,
I think there is a flash front end for it though,
but I think you would need something which plays from a upnp database
But not my build ... yet ...
I'm in the process to rebuild it from scratch and upnp is indeed in my todo list, but I'm under pressure irl too, so you'll need to wait a bit.