Installing alternative PHP cache can greatly improve the speed of your PHP scripts by keeping a compiled version of your scripts in the ram. Installation was done on Ubuntu 8.04 LTS server with a pre-existing apache/php/mysql setup. Run the following commands :

sudo apt-get install apache2-threaded-dev

sudo pecl install apc

echo extension=apc.so > /etc/php5/apache2/conf.d/apc.ini

And restart Apache :

sudo /etc/init.d/apache2 restart