I googled till 4 AM to check how can I enable/install pdo_mysql for magento without the need to reinstall php – as all posts pointed I should do
finally I get it working

From here I started:
1. I already had pdo
2. I hadn’t pdo_mysq;

so back to work (as root):
1. Download PDO_MYSQL from http://pecl.php.net/package/PDO_MYSQL
2. upload it to your server
3. run export PHP_PREFIX="/usr/local/php/"
4. run $PHP_PREFIX/bin/phpize
4. run ./configure '--with-pdo-mysql=shared,/usr' !! /usr was where my mysql was installed (not where the data of mysql are!)
5. make
6. make install
7. in your php.ini
8. add
extension_dir = "/usr/local/php/extensions/no-debug-non-zts-20060613"
extension=pdo_mysql.so
9. restart apache