Client install

May be this is explicitly stated somewhere but I couldn’t find it. I have just installed nagios server and every thing looks fine. Now I want to install a client on another machine which I want to monitor. So on that client machine do I have to install nagios, nagios-plugins? How do I get nrpe? Is it part of nagios or is it a separate package? has the links for extras. Download the nrpe and it comes with excellent docs.