Error Message

In your ./sites/default/settings.php file you have configured Drupal to use a mysql server, however your PHP installation currently does not support this database type.

Environment

I just installed MySQL, PHP, and Drupal-6.9.  PHP and MySQL were installed using 'yum'.  I created a new database and copied another site from my test server as a starting template.  I tried to just hit the URL and got the site offline message.

The site is currently not available due to technical problems. Please try again later. Thank you for your understanding.

Solution

Well, it was pretty easy for me on CentOS.  It helps if you remember to install all the components! 

yum install php-mysql

You might want to install php-gd and php-mbstring too if you have not already.  Give MySQL and Apache a restart and just try it again.  Voila!