How to backup active directory in windows 2003 server?

HI,
I am new to windows 2003 server. I created a active directory with one forest and one domain within the forest. I am not sure how to backup this AD? Do I have to use replication on another windows 2003 server? If yes, do I have to configure a DNS server on the primary DC?

Is there any other way to backup AD or the whole server?

Thanks a lot!