You don't have MySQL's PDO driver in your PHP install. You might just need to add php_pdo_mysql.dll into your php.ini file.
Find your php.ini file and then remove the semicolons from the front of the lines of the extensions you want to install extension=php_pdo_mysql.dll should do the trick.
Find your php.ini file and then remove the semicolons from the front of the lines of the extensions you want to install extension=php_pdo_mysql.dll should do the trick.