The configurable option in Network System Preference to set a DHCP client ID can be overridden by the DHCP server in Mac OS X 10.5 Leopard Server.
Administrators may choose to configure DHCP Client IDs on their network client units in order to statically assign a DHCP provided IP Address to a computer in a specific location. Also, some ISPs required that a DHCP Client ID be configured in order for a DHCP lease to be acquired.
However, if a DHCP Client ID is improperly configured, the network client unit may not properly acquire a DHCP Address. To avoid this, configure your DHCP Server to override the DHCP Client ID settings on network client units.
To configure this feature, edit the server's DHCP configuration file, named "bootpd.conf" located in /private/etc:
After following these steps, as leases are renewed, DHCP Client IDs should be overridden. This should be evident by the absence of Client IDs in Server Admin > DHCP > Clients.