Active Directory

I have two servers on my site and am planning to add a third.
What i need to know is this.

I have one server running Windows 2000 which is running active directory and is the PDC but want to be carefull that it does not crash.

Do i simply install active directory on my new server and run this as a Backup domain controller. Then if my PDC crahses the backup domain controller will kic in and stillallow me to add new users, set permissions etc until i can get my PDC back up and running?

Thanks to all who reply in advacne