Hi,
interesting ... ok ...
check the output of phpinfo. Just below the configuration info is a line shown the configuration file (php.ini) path. Make sure that the php.ini you edited is the one expected by php.
Search for a mysql.so shared library on your system and make sure that the mysql client shared libraries (the mysql-client package) are installed on your system.
Do you get any error messages (printed on the console or written to the apache error log) restarting apache ?
Additionally, you might need to install a package called php4-mysql
Thomas