[Samba] Joining the domain client related questions

[Dennis McLeod]

I have done this in a pure Windows domain. I currently have a Samba server
setup to be the PDC folders are shared, users are added, etc.
Basically the Small office Networking setup from Samba-by-Example on Samba
3.010149 on a Centos 4.4 box.
I have not joined the domain on any machines yet. I'm curious about what is
going to change when I join a workstation to the domain.
These machines have been up, some for a few years. All in the standard XP
workgroup. I understand this is an NT4 style domain, I just don't recall
what happens on the client when I join the domain.
I recall that AD domains created a new profile for the user on the
workstation, like if I had a local account named bob, it would use the
profile in documents and settings named bob. Then when I joined the domain,
it created another bob profile named bob.domain (or something like that).
How do I save the local profile once I join the domain. 
Do I join the domain, logon to the domain, profile gets created, then
reboot, logon local admin, and copy the old profile over the new one?
Or does this not happen?
I'm going to build a machine to test with, but any insight would be
appreciated.
Thanks,
Dennis