DirectInput: sample code won't link in C++, is missing _IID_IDirectInput8A

I find that like my code, the sample code for DirectX 9.0 -- specifically, DirectInput -- won't link.  The file I am trying is C:\DirectX\Samples\C++\DirectInput\dinput.dsw (your path may vary, but it does come with the distribution).  

error LNK2001: unresolved external symbol _IID_IDirectInput8A

Under project: settings, link tab, I find that dinput8.lib is being linked in.  I have tried having it link dxguid.lib as well, but this has not helped.

The line in _my_ code that offends is a call:  
             DirectInput8Create(appInstance,
                               DIRECTINPUT_VERSION,
                               IID_IDirectInput8,
                               (void **)&m_pDI,
                               NULL)
According to http://msdn.microsoft.com/library/default.asp?url=/library/en-us/directx9_c/directx/input/ref/functs/directinput8create.asp, IID_IDirectInput8 is #defined as _IID_IDirectInput8A or _IID_IDirectInput8W.

I am at a college; the PC's in our lab have the same problem -- but the students say they don't have this problem at home.  (My urgency:  some rely on the lab, and they're hitting this problem.)  I am using MS Visual C++ 6.0 and also Visual .NET (same problem).

Thanks!