DHCP Specified DNS Server not Updating on Clients

Here is an odd problem that left me very frustrated and maybe someone has an
idea of what is going wrong:

Domain: Active Directory w/Windows 2003 Domain Controllers and DHCP

I have been in the process of demoting and phasing out my Windows 2k domain
controllers to my new Windows 2003 domain controllers. Weeks ago, I already
made all my dns server changes to my DHCP server scopes to point to the new
domain controllers (well beyond the leases limits). I demoted one of my 2k
controllers yesterday and now this morning I had connectivity issues from
some users that were originally pointed to that old domain controller in DNS
via the DHCP servers. The clients still had the old dns server specified as
the primary dns in their ip settings? I did a release/renew and with the
renew and got the correct assigned dns address, but upon a computer restart
the primary dns would get assigned back to the old. I tried many different
things, but everytime I restarted the computer the client would set it's dns
back to the old server address unless I did a release/renew after startup.
(tried restarting the dhcp services, changing the server list, different dhcp
server, deleting the leases).

The clients were Windows Vista Business; maybe a Vista bug? I did not have
time to check this with an other client OS's.

As a temp. fix, since the old domain controller was still on the lan (just a
member server now), I set forwarders in the dns service to point at the new
domain controllers from the old server; just a 'band-aid' for now.

Any ideas very much appreciated on what's going on since searching around
the net did not turn up much for me...

Thanks
--Chris