I don't really know how to re-broadcast / re-stream web radio stations with Windows Media Services.

If you wanna re-broadcast / re-stream Shoutcast radio stations, you can use a Relay feature of Shoutcast stream rippers.

If I'm not mistaken VLC player can re-stream/re-broadcast to a single host only.

You may try Streaming media proxy and caching solutions, but they seem to be pretty expensive.