Its true that Google will show you the way but here is the steps needed to get you going.
First install the EPEL repo on your server
# rpm -Uvh http://download.fedoraproject.org/pub/e ... noarch.rpm
Then install the package needed with YUM:
# yum install php-mcrypt
Here is the EPEL FAQ
to get you going in the right direction.
Remember to restart apache so the new PHP module is active.