I'd like to offer a possible solution, or at least another factor to look at, for MC12 Media Server problems on a LAN (windows).
I have to run my internet connections thru a proxy server (satellite). I have a utility in the system tray to turn the proxy on and off, but that's a pain. I was having trouble with the "clients" finding the media server unless I remembered to turn of the proxy. I finally discovered that even though I use F.F., MC12 seems to look to I.E. "exceptions" to the proxy. After entering the IP for the media server the clients fire it right up.
I've been using MC now for a long time - I forget my original version - I think I've upgraded two or three times now. It surely has come a long way. In fact, I just bought a new lappy specifically to run MC as my server. Unfortunately, I finally got rid of my old SlimDevces SliMP3 before MC developed that plug-in. Now I might have to get one of those guys fancy, new units too!
Anyway, if you're having problems finding the server, don't forget to check into any proxy stuff you may be using.