Recently I upgraded my Active Directory environment from Windows 2003 x86 to Windows 2008 x64. This is how I migrated DHCP server.
one thing to remember.
Export/Import is the way to migrate from one OS version to another.
Backup/Restore is supported only across similar OS versions.
Export DHCP Data in WINDOWS 2003:
Export the DHCP database from a server that is running Microsoft Windows Server 2003
netsh dhcp server export c:\dhcpdatabase.txt all
Import the DHCP database in Windows 2008
Install DHCP Server, Copy the dhcpdatabase.txt (Backup file that you created on windows 2003 dhcp serverto any folder, Open command prompt, & type
netsh dhcp server import c:\dhcpdatabase.txt all
Authorize the DHCP server, and Restart DHCP Service & you will have all your leases and other dchp related data back online 
For graphical step by step instructions, you can visit.
http://www.it-book.co.uk/2316/migrate-dhcp-from-windows-2003-to-windows-2008-r2
.
Regard’s
Syed Jahanzaib
Can windows 2008 R2 server with 6 Ethernet ports be load balanced and if yes how?
Comment by James — September 19, 2012 @ 4:00 PM