The situation you have at present, is as follows:
You have an NT4 domain, running a single PDC, and no BDC's. You also have a member server which is running 2003.
You are suggesting that you are going to move all the users data from the NT4 server to the 2003 server, and recreate all the necessary shares, and access rights, plus any printers set up on the PDC.
If I have got the above senario correct, then yea, your users will be able to access their files, and still log on with the same passwords and user names.
However, once you switch off the NT4 server, the only copy of the user accounts will no longer be available, and there will no longer be a domain.
If the NT4 server is then returned to the network, once again the domain will be available, and users will still be able to log on.
If you are intending doing this, consider the following.
1. Schedule some down time
2. Copy the files over from the NT4 Server to the 2003 server overnight, possibly with only these two machines on the network (seperate switch) in order to ensure no one accesses the NT4 server
3. Use DCPROMO tool to upgrade the 2003 to an AD domain controller
4. Recreate all user names, shares, and access rights
5. notify users of what their new passwords are.
So often times it happens that we live our lives in chains
And we never even know we have the key