slimserver and firewall

[Gerhard Magnus]

Hello All,

	I'm trying to understand how the client/server interacts with ports and
firewalls by exploring a non-essential application on my home network.
The boxes are running FC4 and are connected to a router behind a DSL
modem.
	The application is slimserver which streams mp3 files over a network to
a piece of hardware called a Squeezebox Network Music Player, which I
don't have.  It can also steam the same files over the Internet to an
mp3 player like xmms running anywhere on the network, which is how I
want to use it.
	The documentation says that slimserver (which I have installed on one
machine) must be reachable via port 9000.  I program the slimserver
playlist (which can include Internet radio) at http://localhost:9000.
The clients (xmms) access the stream at
http://localhost:9000/stream.mp3, where "localhost" is now the name of
the box where slimserver is running.  So far I can play music on the
server machine but not remotely.  
	What place(s) must I open port 9000?  The router?  Each of the client
machines?  How safe is this -- or rather, maybe I should ask, what
precautions are advisable?
	Thanks for the help.  I hope my language isn't too awkward.  Doing
seems to be the only way to really learn this stuff.

Jerry