I'd like to set up shoutcast ( or another service) so I can stream music over my LAN, but I don't want the stream to be announced/delivered outside of my network..... is this possible?

i had set up a shoutcast at work some time back just to see if i could do it. Due to the firewall we have the stream was not accesable from out side the company network. in my case that was bad because i wanted to shoutcast from work where the connection was fast. in your case that would be ideal. unfortunatly i don't remember what i did to set up the shoutcast...but i know it is possible. good luck.

I think you just set it up like regular and have the computers on the network point to the shoutcast server. The firewall keeps other ppl out of it.

In other words, it goes as regular, as far as I know

Monocle and phisherman, you're right.
If you set up a Shoutcast server within a LAN only computers from within the LAN will be able to connect to it, unless you route incoming traffic to go to the right computer and blahblahblah.
So just setting up a server will do, you will only have to do anything special if you want anyone from outside the LAN to connect.