In Windows 2000, DHCP option inheritances uses the following priority, from least specific to most specific:

Default or server option
Scope option
Class option
Reservation option

A more specific option takes precedence. When you remove a more specific option, any less specific option normally takes effect, except in the case of DDNS settings.

The only way to clear DDNS options from a DHCP scope is to use Regedt32 to delete:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\DhcpServer\Configuration\Subnets\<ScopeAddress>\SubnetOptions\081

where <ScopeAddress> is the address of the scope.

Stop and restart the DHCP server service.