argument

I got a ActiveX Control method
[HRESULT GlobalDictation(VARIANT hwndApp, VARIANT_BOOL Enable)]
hwndApp Optional window handle of the application for which to enable or disable global dictation.

I hope to put my application's active window handle to the first argument "VARIANT hwndApp". I try to use the CWnd* GetActiveWindow() function in MFC. But I do not know how to cast the CWnd * to VARIANT. Could somebody tell me what I should do (include initializing) to put the active window handle to the argument "VARIANT hwndApp"?
Thanks.