Windows Services for Unix. I think the first time I saw it was around 2001/2002 they've gone through several revisions adding features. You know the Microsoft Motto, "Embrace, Extend, Assimilate, Exterminate" I think that's why it's FREE...
I have not actually used them myself, but I can't see MS having a product out for that long and it not working.. (ok no need to hit me over the head with windows ME, or MS Bob, or any one of their other wonderful products

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Look at how well their Certification program (MCSE NT4) to Migrate from Netware worked ... But seriously though it should work very well, I've just never had a need to use it.