Starting with Visual Studio 2010, Microsoft decided to make life hard on C++ developers. System-wide include path settings used to be accessed through Tools | Options | Projects and Solutions | VC++ Directories. However, that option is gone:
Instead, the system-wide include paths are now located within the ‘Properties’ interface. To access it, select View | Property Manager. No dialog will appear yet. Instead, the Property Manager appears as a tab along with the Solution Explorer:
Note: The Property Manager won’t contain anything unless a solution is loaded.
Now, expand one of your projects, then expand Debug | Win32 or Release | Win32:
Right click Microsoft.Cpp.Win32.user and select Properties:
This brings up the Microsoft.Cpp.Win32.User Property Pages dialog, which should look familiar enough:
The properties can be accessed directly as an XML file by editing%LOCALAPPDATA%\Microsoft\MSBuild\v4.0\Microsoft.Cpp.Win32.user.props