samba - Feb 2010 - Can one user use the same credentials to log into multiple domains, and how do I do it?

First, our current setup.

I'm setting up a Samba 3.4 environment to replace our old Samba 3.0.x setup
and make ready for Windows 7. There are several different campus locations, and
each has it's own Samba PDC. Due to some (possibly poor) decisions made
early in the development of the system, instead of giving each campus its own
domain name, we used the algorithmic rid base parameter in smb.conf to manually
beat on the numbers to make it work.

I believe this is what would fix the problem, but Anyway, here's my problem.
I have the new Samba server set up with a different domain name and it appears
to be working, but now users from the old domain setup can't log in. It
looks like it's an SID problem, as the log messages are similar to:

--snip--
[2010/02/18 09:53:46,  1] rpc_client/init_netlogon.c:237(serverinfo_to_SamInfo3)
  _netr_LogonSamLogon: user DOMAINNAME\username has user sid
S-*-*-**-**********-*********-**********-*****
   but group sid S-*-*-**-**********-*********-**********-*****.
  The conflicting domain portions are not supported for NETLOGON calls
--/snip--

Sure enough, the *'d out SID's are different, the first is the SID for
the old domain, and the second is for the new domain. Now, I could just go and
change the user's SID but there are a couple of problems with that. One,
that's problematic for a system with several thousand users. Two, even if I
were to do that, we have several users who move between campuses and would need
to log in to several different domains, and changing SID's when they move
would also be problematic. Maybe this is what a "roaming profile" or
"trusted domain" is, but I'm not sure.

So here's my question: How can I set Samba up to accept logins on one domain
with credentials from another, or is this even what I would need to get this
working?

Thanks,
Johnathan

--
Johnathan Bell
Internet System Administrator, Baker College