Is the "xsd" command not supported in Visual Studio 2012 command window?

xsd.exe is available from the 'Developer Command Prompt for VS2012, not the command window that is part of the VS2012 IDE.

The 'Developer Command Prompt for VS2012' itself can be started from Start Menu -> All Programs -> Microsoft Visual Studio 2012 -> Visual Studio Tools -> Visual Studio Command Prompt For VS2012

Under Visual Studio 2012, there is a feature called Past Special which generate the class from an xml file.

See here: Paste XML or JSON as classes in Visual Studio.

Note that this feature requires at least .NET 4.5.