This works for me on CentOS 5.8
You will want to do the following as root:
yum install net-snmp
Then you will want to edit /etc/snmp/snmpd.conf to configure the service.
So that the service will start on boot, you will need to:
chkconfig snmpd on
And lastly:
service snmpd start
#############################
# my own notes:
Here is a super simple snmpd.conf file that works fine:
rocommunity public 192.168.0.0/24
rocommunity public localhost
I needed to add this line in /etc/sysconfig/iptables
-A RH-Firewall-1-INPUT -m state --state NEW -m udp -p udp --dport 161 -j ACCEPT
and restart iptables with /etc/init.d/iptables restart