exchange 2000

1. Using windows 2000 with AD, ForestPrep, domainprep were done. Where do I set permission so that I could include “Exchange(M:\) where MBX and public folders are” to my backup? If I do backup, it says “no permission to access” and skipped the backup.
I have included the administrator with Full control on all the mailrights. I could view ,open mailboxes but can not backup.
2. I did replication on second machine – but I have noticed that mailboxes where not replicated, users set up on AD were all replicated. I did a test, I shut down the Primary Active Directory, the seconday AD is on, clients could not use exchange. What should I do about the DNS?