I am trying out magento in my CentOS 5.6. The php minimum requirement is 5.2 and CentOS 5.6 adds php53 as a php replacement, which is not installed by default.
To install php53, remove the installed php5.1 first.
yum -y remove php*
Install php53 and some common extensions.
yum -y install php53 php53-mysql php53-xml php53-gd
When I tried to install php53-mcrypt, it returned that package not available, so I must build it by myself.
Install php53-devel and libmcrypt-devel first
yum -y install php53-devel libmcrypt-devel
Download the php 5.3.3 source code from php.net.
Next add the following line to php.ini
Restart your apache