Just a silly question, but... did you log into the Win2K system as "Administrator"?
I beat my head against the wall for 2 hours trying to figure out why it wouldn't work after the Samba upgrade - the whole time, I was logged into the Win2K system as a user with admin priveleges, not the administrator account. Once I logged out and back into the Win2K system as "administrator", I was fondly rewarded with "Welcome to the XXXXXXX Domain" when I added the workstation to the domain.
Cheers!
Ari