DHCP supports three different mechanisms for IP address allocation:

Manual allocation: the server's administrator creates a configuration for the server that includes the MAC address and IP address of each DHCP client that will be able to get an address: functionally equivalent to BOOTP though the protocol is incompatible.

Automatic allocation: the server's administrator creates a configuration for the server that includes only IP addresses, which it gives out to clients. An IP address, once associated with a MAC address, is permanently associated with it until the server's administrator intervenes.

Dynamic allocation: like automatic allocation except that the server will track leases and give IP addresses whose lease has expired to other DHCP clients

How can i configure the automatic allocation on Windows 2000 or XP DHCP server?

i can think of setting the lease to unlimited period, but i m not sure if the computer shutsdown gracefully it will make the ip address available to other machine.