The Migration Tool for NetWare--included with Microsoft's File and Print Services for NetWare (FPNW)--is a one-time process that moves user and resource information from a NetWare server to a Windows NT server. Once that information has been migrated, any changes made to the NT Server user/resource settings won't be reflected in the NetWare server configuration. Similarly, any changes made to the NetWare server user/resource settings won't show up in the NT Server configuration. In short, the migration tool is oriented toward turning off the NetWare server for good.
In some cases, it may be necessary--even desirable--to maintain a mixed network of NT servers and NetWare servers. This is the environment addressed by Microsoft's Directory Service Manager for NetWare. Like the Migration Tool, the Directory Service Manager allows you to migrate user and group information from a NetWare 2.x or 3.x server. Unlike the Migration Tool, however, any changes you make to NetWare users or any new NetWare users you add are sent back to the NetWare server, keeping the NT and NetWare server information in synch.
The Directory Service Manager doesn't require using FPNW, although they can certainly work together. There are two primary advantages to the Directory Service Manager:
(Note that the Directory Service Manager doesn't provide all the functionality that Migration Tool for NetWare offers. In particular, it doesn't transfer logon scripts or other resource-related configuration information.