2000 to 2003 server upgrade problems

Environment:
Native windows 2000 network with 2 DC.
Events:
Run adprep /forestprep appeared succesful
Run adprep /dpmainprep appeared successful
Run inplace 2003 upgrade on DC.
Found & installed SCSI drivers OK.
Completed upgrade without being requested for 2003 NIC drivers.
On completion no network connectivity.
Found & installed correct NIC drivers.
Installed SP1 OK.

Other DC is still Win2000
Upgraded server can connect to other network shares OK.

Problem:
1. All other network machines cannot connect to 2003 server shares - username & password requested but not accepted.

2. Removed AD to make Win 2003 server a member.
All other machines can now map to 2003 server shares but not write to the shares (Read & Execute only) while as a member server.

3. Run dcpromo to add AD reverts back to problem number 1.

Any help very much appreciated