When I moved some workspaces over from another domain  I used Microsoft's
export and import tools. First of all I created the sharepoint  groups on the
new domain that existed on the old domain and populated them with correct
users.The export tool creates an XML stub for each workspace and I replaced
the old domain name with the new one in the XML file. You do loose
discussions etc when using these tools but it depends if you had implemented
discussions. This only really works if you have implemented groups and not
just put users  on an individual bases on to every folder within sharepoint Also I'd like to mention at this point that every sharepoint
installation is different so try a test first!!

The same was that we projected also for the same problem ; but we experienced
that sps  exim tools doesn't work, so I asked this list for a prog which changes
the roles. You can see the letters about this subject on the week before last.

Yes; actually what we are going to do is write some code in a VB
Windows application, in order  to:
- access a folder thru CDO
- access the various arrays (Readers, Authors, Coordinators)
- for each entry, match the "old login" with the "new AD login"
- add the new login to the array

We are choosing this way because we will not migrate  every user  in a
single run: we want to migrate, say, 10 users  every day (migrating
also their mail, their access rigths to file system resources, etc).

And we do not want, for a while, to lose the old access list.

If you are interested in our code drop me a mail; all this is in a
developing and testing phase, but we think to have the code complete
in 1-2 weeks.