HELP WITH WINDOWS 2000 UPGRADE

Hello,
I intend setting up a new server with windows 2000. I am presently using Windows NT 4.0 server with all the user accounts already created. How can I migrate the present user accounts from the NT server to the new Windows 2000 server?

Alsoafter upgrading my present windows NT4.0 server with a partition size of 4GB to Windows 2000 it still retains the 4GB size. How can I enlarge the size from 4GB? I have a hard disk of about 18GB.