Perform these steps from new W2K8 DHCP server:
1.Open DHCP mmc
2.Open Command prompt: cmd
3.Type: netsh dhcp server export C:\dhcp.txt all in command prompt and press Enter
4.Delete ALL scope information from within the DHCP mmc
5.Type: netsh dhcp server import C:\dhcp.txt all in command prompt and press Enter
6.Right-click server name within DHCP mmc and choose refresh
At this point I was able to view all of my Address Leases. All entries had a Name that was equal to its Client IP Address, a Lease Expiration of the time of my export, a Type of DHCP/BOOTP, and a very long Unique ID (32 characters). After performing a "Ipconfig /renew" from a workstation, the workstation's Name appeared correctly, the Type changed to just DHCP, and the Unique ID was the MAC address of the workstation.
I then created a command file (renew.cmd) with the command Ipconfig/renew as the only contents. I placed this file on a UNC path (\fileserver\sharename\renew.cmd) that I knew all domain users had access to and then sent them an email with the link to the file and instructions to select "Open" after clicking the link. The proper DHCP registrations just started rolling in after that.
Copied from: http://social.technet.microsoft.com/Forums/en-US/winserverNIS/thread/1b8cd762-3f95-4ff9-9d9e-75b04e067d2a