I'm not an expert on Internet Radio by any means and its one area I'd like to learn more about! I've seen various Internet Radio plug-ins for VMC but I've never really used any. I've recently been listening to 80's music radio stations on Shoutcast however on my Sony PSP, I did a PSP update recently and a new Internet Radio feature appeared and is driven using Shoutcast.
Sornt from German has written a Shoutcast Internet Radio plug-in for VMC called mcShoutCast, which looks pretty interesting. More details can be found here. The screen shots are in German but I believe there is an English version as well. No official support for extenders however from the author.
I think I will have to look in to some of these VMC Internet Radio plug-ins in more detail and give a few a go.