Are you sure you enabled mysql in the php installation?
To check taht, create a small php page, that will look like this :
Code:
<?php
phpinfo();
?>
This will give you all info you need about the installed php.
Check that in the "Configure Command" row you have "--with-mysql".
If not, you'll have to recompile and add this option (or install a package named php-mysql) so that php can connect with mysql.
Good luck.