Primary DNS Secondary DNS! Whats the point?

In my windows domain, I have two domain controllers, and both are configured as DNS servers. DC-01 is set as the primary DNS and DC-02 is set as the secondary DNS. Everything works fine and the DNS updates are quick to both servers. The problem is, when I have to take DC-01 down for some reason, no PC on the domain can resolve DNS until the primary is back up. Should it fall back on the secondary DNS if the first is unavailable? Am I missing something? Both DC’s are Server 2008 and all of the clients are XP Pro SP3.

Thanks in advance for any enlightenment!