Sever 2003-2008 migration, migrating primary DNS, not secondary: client issues?

My network has two Server 2003 domain controllers, no Exchange, no SBS. One (DC1) is the primary DNS, the other (DC2) is a secondary DNS. A new Server 2008 (DC3) is now a member server, waiting to be promoted. I have already run adprep commands on DC1.  I am going to promote DC3 today to be a domain controller, and hopefully transfer the DNS and DHCP from DC1  to DC3.   The clients with DHCP should be fine, I assume, but I have a number of reserved IP numbers for fixed IP's on various computers and other equipment.  The fixed IP clients point to DC1 and DC2 to as their DNS. After the migration, DC1 will be demoted but will remain on the network.  

I am pretty much in uncharted territory here, have only built from scratch in the past, and am not sure what issues the clients will see, especially the fixed IP clients, most of which are XP.  Will they see no down time at all, since they also point to DC2? That would give me time to change their DNS settings at leisure.  Will they get a DNS error at startup when one of their DNS's is no longer a DNS and there is a new DNS out there?  I am especially concerned because I did not have an opportunity to warn the users this was coming.
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As long as Secondary DNS server will be availiable, clients will fully function and receive no errors.
Latter you can change DNS setting via command line - psexec to connect to another computer and netsh to change settings, or deploy a GPO to do it for you while computer is starting.

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SusanSBAuthor Commented:
Thank you Vaidas911.  This has definitely made the day easier.
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Windows Server 2008

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