I have doing some installs of CentOS 5, and I have come across a couple of problems,
1) it seems that the Mysql install is either incomplete or doesn’t work so it was necessary to get the latest version using yum.
yum install php-mysql mysql mysql-server
/sbin/chkconfig --levels 235 mysqld on
and 2) The php build while it is a recent one does not include the php-mysql drivers. So the ‘php-mysql’ will install the mysql drivers.
Hope this helps somebody because it took me a little while to find it.