Nagios Missing Dependency: perl(Net::SNMP)

Which Nagios packages do you have installed? On my CentOS 5.4 boxes, the Nagios config is in /etc/nagios. Take a look there. The filename is /etc/nagios/nagios.cfg

Edit

On the remote side, you need an entry in the nrpe.cfg that looks like command[something]=/some/path/to/command/binary. Then, on the Nagios host, you do your define service { }. The important part is that the command to run is going to look like check_nrpe!something, where something is the same as the one in nrpe.cfg.

SNMP is available for everything, Linux, Unix, Windows, Cisco.. and many more.

Certain information will be available on NRPE that isn't on SNMP. Your setup time with snmpd will be allot quicker, once you get your head around how SNMP works.

You can provide a snmpd.conf config to your clients and they can setup their own snmp daemon quickly and without too much trouble shooting on your behalf. I imagine you requesting access to clients servers to install NRPE. Depending on your install method, your clients systems may not be keeping NRPE up-to-date, unlike snmp which is very mature and guaranteed to be maintained by the distributions package management system!

save yourself some effort and avoid using NRPE unless snmp can not provide Nagios with the correct information.