What are the benefits of using Windows 2003 DNS when using AD-integrated zones?

Multimaster update and enhanced security based on the capabilities of Active Directory. 

Directory replication is faster and more efficient than standard DNS replication. 

Zones are replicated and synchronized to new domain controllers automatically whenever a new one is added to an Active Directory domain.

By integrating storage of your DNS zone databases in Active Directory, you can streamline database replication planning for your network. 

if you have more than one domain controller (recommended) you need not worry about zone replication. Active Directory replication will take care of DNS zone replication also.

• If your network use DHCP with Active Directory then no other DHCP will be able to service client requests coming from different network. It is because DHCP server is authorized in AD and will be the only server to participate on network to provide IP Address information to client machines.Moreover, you can use NT4 DNS with Service Pack4 or later. It supports both SRV record registration and Dynamic Updates.