$ sudo aptitude install apache2-mpm-prefork mysql-server php5-mysql cvs
yup this is enough to install php-mysql extension
its better to run this command "sudo apt-get update" before installing a new software/package
Also do "sudo a2enmod rewrite" to enable clean url
Ubuntu is not using httpd.conf instead its using 000-default as configuration file where you can change your document root, overridding and other things