Instalar PHP en Centos 6
Para instalar PHP en Centos 6 lo primero es tener el repositorio de EPEL, para ello como root desde una consola ejecutar:
rpm -Uvh http://download.fedoraproject.org/pub/epel/6/i386/epel-release-6-7.noarch.rpm
Luego instalar PHP con algunos modulos adicionales:
yum -y install php php-mysql php-common php-gd php-mbstring php-mcrypt php-devel php-xml
A couple of notes, sazitine your request variables before pulling data directing into you code. Avoid using double quote for simple string echo as it is extra load on php parsing use single quote instead. Play with MVC type frameworks such as Zends framework to get familiar with design patterns. Nice tutorial for beginners but be warned, I had to fire a bunch of people recently who programmed like this go back to programming basics and learn popular framework methodologies.