The first part is really easy; you install MS Windows 2000 server & SQL server on the new windows server, and connect it to the network. For your size network, I STRONGLY recommend configuring it as a "stand-alone" or "workgroup" server -- avoid installing Acive Directory. Install only the IP protocol on the server.
Then, at each client workstation, install the client for microsoft networks. Make sure each workstation's workgroup name agrees with the server. Make sure the workstations have TCP/IP configured. If you don't already have one, now is a golden opportunity to add a DHCP server to your network if you can.
Create shares on the Windows 2000 server
Last but now least, add user accounts to the Windows server. The concepts for users and groups are similar between the two, although Windows won't give you the control or granularity you're used to in NDS.
If you make the user name & password on the Win2K box match the user name and password from netware, the user won't be prompted for them when they connect to a share on the Windows server.
One tool that makes that last step very easy is Synchronicity from NetVision (http://www.netvision.com/products/synchronicity.html)
Baically, Synchronicity synchronized user ID's and passwords between the windows server and NDS. When you use NWADMIN to create or change a user, it automatically updates the Windows user database.
HTH