SELinux configuration file on CentOS is located at
change "SELINUX=enforcing" to "SELINUX=disabled" (takes effect after next reboot)
Security-Enhanced Linux, also know as SELinux, implements various security policies on Linux and additional levels of access crontrol. It was originally developed by the U.S. National Security Agency to adhere to the "Orange Book" guidelines. On CentOS 5 it is enabled by default
In "normal" linux there are really only two major categories of users, administrators and non-administrators. In order for services and programs to run with any level of elevated privilege, the choices are complex and and typically involve either giving full admin access or setting up custom groups and setting lots of different permissions.
Solutions such as ACLs (access control lists) can provide some additional security for allowing non-administrators expanded privileges, but for the most part a root account has complete discretion over the file system.
SELinux defines permissions for how Subjects (processes) can interact with Objects (files, devices, ports, etc.)
By Default SELinux only "restricts" a very specific set of daemons (known to be popular targets) and leaves all others in an unconfined state (thus you can implement the granular controls yourself).