This version of PHP is the default one that comes with this version, 5.2.3. Check you have installed the php5-common package from aptitude as this includes the pdo.so file. If you check phpinfo you should see that PDO is listed as a module although you don't have any drivers.
Then you should do:
sudo aptitude install php5-mysql
Restart apache and check its error log in case there are any problems. Then simply refresh your phpinfo page and pdo_mysql should be listed.
For earlier versions of ubuntu/kubuntu have a look at this excellent tutorial from theatons, I followed this but its slightly out of date now which is why I've posted an update. Most of the rest of the tutorial is still correct though.