DHCP and RAS issue

I am running a Windows 2000 server environment. I have 4 buildings in my WAN each has its own subnet in the network. The DHCP lease availability on one of these fills up every day. When checking the statistics for the subnet I see the computers who are logged in and granted the host lease; I also show a duplicate with a RAS unique identifier. This literally fills up the subnet each day and of course locks up any new attempts to join anything else to the domain. The question is how do I stop these RAS duplications.
Thanks.