Try locating and setting the following parameter in your php.ini (it is in the Dynamic Extensions section):
extension=php_mysql.dll
prior to this change, I could make a simple php script without mysql run, like this
<?php
phpinfo(();
?>
but not another one like this
<?php
echo mysql_connect ('localhost', '<yourwebuser>', '<yourwebuserpassword>');
?>
the previous should normally output something like:
Resource id #n
where n=1 or 2 or