BuddyPress.org

If you are using WP MU (multisite…or whatever you like to call it), then you can do this easily at: http://yourdomain.com/wp-admin/ms-options.php Things like this is why I’ve installed my BP on WPMU even though I don’t use more than one blog. The good thing is that since WP 3.0 you can switch to MU easily. Just be sure to test it first and do a good backup.

I want to say there was some way to hack WP single install, but I can’t remember.

Try this: http://www.wpbeginner.com/wp-tutorials/how-to-enable-multi-site-option-in-wordpress-3-0/

Be sure to back up your site before you do it.