Within the DHCP snap-in, I have many DHCP reserverations in my list of address leases. Some of these reservations I suspect are ancient and are not being used any more. Under Address Leases, some of the leases are marked as Reservation (inactive)
in the Lease Expiration column. Is there a way to see the last time that an inactive lease was indeed active?
If you search for the MAC address in the plain text log files at this path:
%system32%\dhcp\DhcpSrvLog.*
...you will be able to see each time that MAC address checked in with the server within the last 7 days. Note that I tried this on a Server 2000 machine -- the path may be slightly different in a 2003 environment.
To find the MAC address, you can look it up in the DHCP reservation or run
ipconfig /all
on the computer with the reservation.