As per usual, the majority of the code will be written in Microsoft's "interpretation" of C++

Some of the legacy stuff was probably written in ISO C.

From what I've seen, its still unclear with Longhorn will contain DotNet, but if it does, then its inevitable that "less essential" parts of the OS will have been written in CLR languages, C# and Managed C++ most likely.

I wouldn't be surprised to see bits of Windows written in Objective-C or Delphi though Wink