This post is more for personal reference as I couldn’t find anything definitive online for installing PHP and MySQL on RHEL5.5 easily.

sudo -s
wget http://download.fedora.redhat.com/pub/epel/5/i386/epel-release-5-3.noarch.rpm
wget http://rpms.famillecollet.com/enterprise/remi-release-5.rpm
rpm -Uvh remi-release-5*.rpm epel-release-5*.rpm

yum update

yum install php php-devel php-mysql php-gd php-imap php-xml php-odbc  php-mssql

Hopefully someone else will find this useful