You will need to install the Extra Packages for Enterprise Linux (EPEL) rpm which can be found at:
'rpm -ivh http://download.fedora.redhat.com/pub/epel/5/i386/epel-release-5-3.noarch.rpm' for i386
or: 'rpm -ivh http://download.fedora.redhat.com/pub/epel/5/x86_64/repoview/epel-release.html' for 64bit.

Once the EPEL rpm has been installed, you will then be able to install mod_security by typing 'yum install mod_security' and restart the Apache service.

Make sure that the mod_security engine is turned on by going to
/etc/httpd/modsecurity.d/modsecurity_crs_10_config.conf and look for 'SecRuleEngine On'

One of the coolest features is masking the server signature of Apache. This can be done by editing the httpd.conf and making sure that 'ServerTokens' is set to 'Full'. Then change 'SecServerSignature' in 'modsecurity_crs_10_config.conf' to whatever you want.