Is this possible in NT (I know it can be

Answer 1 is correct in so much that you can’t block the other IP Addresses, however, another workaround if you want to keep DHCP is to add a reservation to all the addresses in your scope and as and when you have a new machine put the MAC address into one of the reserved addresses.
I know this removes some of the flexibility of DHCP but at least you will still have a single point of administration.