How to install drupal on Ubuntu

The following commands issued on the commandline, should install drupal on ubuntu assuming you have the dependencies (apache, php, etc)

wget http://ftp.drupal.org/files/projects/drupal-6.9.tar.gz
tar xvzf drupal-6.9.tar.gz
sudo mkdir /var/www/drupal
sudo mv drupal-6.9/* drupal-6.9/.htaccess /var/www/drupal
sudo mkdir /var/www/drupal/sites/default/files
sudo chown www-data:www-data /var/www/drupal/sites/default/files
sudo cp /var/www/drupal/sites/default/default.settings.php /var/www/drupal/sites/default/settings.php
sudo chown www-data:www-data /var/www/drupal/sites/default/settings.php
mysqladmin -u root -p create drupal
mysql -u root -p
sudo /etc/init.d/apache2 restart

IF....
php isn't installed correctly.

you could try installing it as a module

sudo a2enmod
php5