So we have a Server 2003 DC(call it ServerA) with DNS and DCHP. After extending our schema, we'll be introducing a Server 2008 DC (call it ServerB) along with DNS and DHCP. After promoting ServerB as DC, transferring zones from ServerA to ServerB, and moving the DHCP database from ServerA to ServerB, do you think it's better to get rid of DHCP and DNS from ServerA or disable these two for the moment? I would like to ensure that ServerB will be able to hand and resolve IPs before getting rid of DNS and DHCP from ServerA. Thanks guys!

I would get disable DHCP but I would keep DNS on the server if you are going to run AD services on this server still. If you aren't going to keep AD services on this server then I would wait to remove DNS when you remove AD services. Make sure your new DC is a global catalog and that you have transferred your FSMO roles to the new server. http://www.petri.co.il/transferring_fsmo_roles.htm Run dcdiag to check for any errors before transferring roles and after. Then make sure you change your DHCP scope so it is leasing an IP Scheme with the new server as the primary DNS Server

If Server A will remain on the network, I would consider running DNS and DHCP on both servers (maybe re-install the 2003 box and create another 2008 DC). That way you have fault-tolerant for DNS as well as DHCP (50/50 scope split). In any case, to answer your question, you can simply stop the services (set them also to manual) on Server A until you are sure that the migration of the services has been completed. Visit: anITKB.com, an IT Knowledge Base.

I'll definitely disable both DNS and DHCP on ServerA until I can ensure that things have been migrated over. If ServerB has hiccups, I can enable DNS and DHCP on ServerA and everything will work fine.