Registration redirect

I'm using WPMU 2.9.1, BuddyPress 1.1.3 and BBPress 1.0.2 and Social for the theme

I've installed all of these manually. The only problem I'm having is the redirect link for registration. Currently the registration link on the main page goes to and the landing page is for hosting service. It doesn't matter if I have registration enabled ofr disabled the redirect remains.

I also don't understand how to do the following:

"If registration is disabled, please set "NOBLOGREDIRECT" in wp-config.php to a url you will redirect visitors to if they visit a non existent blog."

I've been into wp-config.php and found where "NOBLOGREDIRECT" is but not sure how to set it.

Any help would be greatly appreciated, thank you. I won't be back online for about 3 hours.