Darren has written an article on some of the challenges and issues that you may encounter when migrating from Novell NDS to Windows Active Directory. It can be quite a complicated process which will fail without the right level of planning and testing. He discusses the different types of migrations, with the pro's and cons of each type of migration, he also discusses the Microsoft MSDSS tool and Quest NDS migrator. There's a good explanation of how the concepts of NDS translate to Active Directory, especially around X500 naming conventions and password migration.
here's his article