Hi Paul,
There are many ways you can configure SAMBA. Back before Microsoft started churning its OS, you could have a Linux samba server join a windows domain. All authentication then occurred on a Windows NT 4.0 server, and users added to the Linux computer would automatically have an account created on the Windows Domain Server (eg DNS).
Since Microsoft's introduction of active directory, I'm not sure if a Linux SAMBA server can still join a domain administered by a windows 2000 DNS.
You can centralize authentication in a windows network by letting a Linux samba server become the network's DNS, but a Linux DNS emulates a windows NT 4.0 server, which might not give full benefits to an otherwise mainly windows network utilizing active directory.
I'm sure the samba folks are working on all this, but I haven't done anything recently with samba, and I don't know exactly how advanced samba has become in addressing the issue of Microsoft new stuff. I'm primarily a Linux Network, but I still have a windows NT 4.0 DNS for authentication, at least for folks booting into windows. Otherwise I'm using Sun's YP service, (eg Yellow Pages), to centralize authentication of logins to Linux computers.
I was thinking you could check the samba mail list to find the current status of samba in addressing this issue. Then you might post back to let others following this thread know what you find out.
Regards,
LelandJ