On CentOS 6 I cannot install GeoIP even though many websites describe installing GeoIP with the following commands:
yum install GeoIP GeoIP-devel GeoIP-data
No package GeoIP available.
Seems like you need to add an additional repository. In CentOS5 the Geoip stuff was located in Centos Extras. Check out this link: http://wiki.centos.org/AdditionalResources/Repositories
If the package is not in Extras try out the EPEL repo (howto is in the link above), they have the packages: http://dl.fedoraproject.org/pub/epel/6/x86_64/repoview/letter_g.group.html