dhcp and dynamic dns

I have a LAN setup of win2k clients with a linux debian server. The linux
server dishes out ips using dhcp and provides name resolution using bind9.
The problem is that the 2k clients delete the records when they shutdown. I
need at least for the reverse records to remain so that when the squid logs
are batch processed the reverse lookups work.

I would most grateful in being able to sort this out at the server side. I
am aware that there may be a way of altering the win2k client's registry/dns
settings so that the dns records are not deleted when the machine is
shutdown - only when the lease is released.

Thanks in advance.