better performance= using associative arrays;

config.php:

$config['username'] = 'faganon';
$config['password'] = '2hacker4u';
$config['hostname'] = 'db.gtfo.org';

so, main.php

(NEVER require. use require_once or include_once. unless you want to get redefining shit errors.)

include_once('config.php')
mysql_shit($config['hostname'], $blahblah);

if that fails, you can also try var_dump($config);