GreNME said:You would be wrong on both counts. It was written from the ground up, though the parts in development that may seem very close to, say, OS/2 would be because most of the core development team that created it were brought on board by Microsoft to develop the NT operating system into what was eventually (mostly) fully realized with Windows 2000 (prior versions were close but not "all the way there").
Actually, internally OS/2 and Windows NT were (are) not very similar at all. The only code that they really shared was in the Win16 and OS/2 subsystems. Other than that you are correct in that NT was written from the ground up mostly. However, architecturally it does resemble VMS far more than it does OS/2 or *nix, again largely due to the influence of Dave Cutler . More references:
http://www.windowsitpro.com/Articles/Index.cfm?IssueID=97&ArticleID=4494
http://www3.sympatico.ca/n.rieck/docs/Windows-NT_is_VMS_re-implemented.html
http://www.microsoft.com/PressPass/exec/de/default.asp#DaveCutler