You can stream net radio with VLC, share files over torrent or other p2p networks set up ftp server.
But sharing music may be pirating. Be careful.
I have a PC connected to my Router that is running WInXP. As you can imagine, in my amateur days, I set up music sharing via iTunes. I just got a new laptop with a 2.2 gHz processor/4GB RAM. I set it up with a beautiful dual-boot Ubuntu and Win7. However the new versions of iTunes don't allow any other program to pick up the music on the network. Is there a program that can pick up the itunes music or maybe a program that has linux and windows versions that can share my music?
I have tried to put iTunes on WINE, but it did not pick up my shared music on the network.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic