Check your PHP Setup for MySQL support
<? phpinfo() ?>
If not enabled
Some possible ways to enable MySQL support:

apt-get install php-mysql
rpm -Uvh php-mysql-4.2.2-1.i386.rpm

./configure --with-mysql=shared,/usr
cp modules/mysql.so /usr/local/lib/php
extension_dir=/usr/local/lib/php
extension=mysql.so