Calling COM Objects In C++ Using CoCreateInstance(...)

Variants of this question have been asked several times.  How do you call functions from a COM object created with Visual Basic (or anything else for that matter) from C++?

Well, it's not too difficult if you implement MFC and use InvokeHelper(...) and CreateControl(...) functions.  However, I'm trying to do it using straight C++ without MFC.  The really tough part is I don't have a header file either, so I don't even have an abstact class to work with!

Here's the equivalent of what I'm trying to do in VB:

Dim myobj As VicNet.VicNetCtl

Set myobj = GetObject(,"VicNet.VicNetCtl")

myobj.Function1("abc")

Pretty simple, eh?  Create a control called "VicNet.VicNetCtl" and then call a function that it exposes.  Now, how do you do it in C++ without MFC or a header file with an abstract class definition?

Here's what I have so far:

void main(int argc,char *argv[])
{
  CLSID vicnetCLSID;
  IDispatch *myobj;

  CoInitialize(NULL);
  CLSIDFromProgID(L"VicNet.VicNetCtl",&vicnetCLSID);
  CoCreateInstance(vicnetCLSID,NULL,CLSCTX_INPROC_SERVER,IID_IDispatch,(void **)&myobj);
  myobj->Function1("abc");
  CoUninitialize();
}

Of course, the first thing that breaks is IID_IDispatch is not declared.  So perhaps I should use IID_IUnknown?  Also, our pointer myobj doesn't know about Function1().  So how do I call the function?

Maybe I'm missing the obvious, but I can't seem to think right now.