My name is Johnny Hughes. I am one of the lead developers at the CentOS Project, which releases the Linux operating system called CentOS. I am currently the Project Lead on the CentOS-4 version of the distribution.
The current release of CentOS 4 is version 4.8 which was released on August, 21st 2009.
CentOS 4 will be supported with security updates until February 29, 2012, although if you are planning a new deployment you should probably use the latest version of CentOS, currently CentOS 5. CentOS rebuilds sources from Red Hat Enterprise Linux, and will release updates as long as they are released upstream. For Red Hat's policies and lifetimes, please see this link.
If you are looking for help with CentOS please see Getting Help on the CentOS Wiki.