Configuration network connection with JMS

Hi,
I have a JMS application working fine locally but I want to make it work between different machines. Until now, my publisher looks up into a jndi property file to find the connector "provider.url=vm:broker:(tcp://localhost:61616)".

I'm pretty new to ActiveMQ and JMS and I'd like to know what should I configure to do this (and how).
For example, can I create brokers within the JNDI properties files or is it better to do it in Java?
Do I need to use a server between the JMS publishers and subcribers to transport the messages or does ActiveMQ manage this?
Many Thanks
Snake