I was searching around on how to Enable Multisite on WordPress 3.0 RC1 and I couldn’t find anything, and some sites were incorrectly telling you how.

Here is the official instruction’s from WordPress on their Codex site.

http://codex.wordpress.org/User:Andrea/Create_A_Network

All you need to do is add the following code into your wp-config.php

define(‘WP_ALLOW_MULTISITE’, true);