On the existing DHCP Server, open a command prompt and enter the following command:
netsh dhcp server export C:\dhcp.txt all
Copy the file to the new DHCP Server and then open a command prompt and enter the following command:
netsh dhcp server import c:\dhcp.txt all
This works with Windows Server 2003 and 2008.
Reference: http://technet.microsoft.com/en-us/library/cc772372(WS.10).aspx