This isn't the answer you're looking for, but the "web media" part of MC is not as polished as the rest of the program. I also tried adding a couple stations a while back, but I never saw them show up in the list. When the list eventually became severely out of date (LOTS of stations that could no longer connect) I finally gave up on it.
Fortunately, MC's flexibility offers another way to manage web radion stations. I use sites like shoutcast to open radio stations in MC (or cut and paste their URLs into the "open URL" window of MC), then I edit the tags for each station in the Playing Now screen and import the file into my library under the genre "Web Radio." To organize the stations, I use the Artist field as a secondary genre field (i.e. "Web Radio - Rock/Pop" or "Web Radio - Blues," etc.) and the Ablum field for the name of the station.
This system of orginizing web radion stations actually works really well -- I highlight "Web Radio" in the genre pane, then select a "sub" genre in the next pane (the Artist pane), then select the radio station in the next pane (Album pane.) If the radio station broadcasts the song title, it shows up in the track list.
One of the really nice features of this organizational method is that I can browse and access web radio stations in Theater View mode, which is not possible with the "Web Media" section of MC. I can now access web radio stations in Theater View mode the same way I access mp3's, which is a terrific feature.
Larry