IXMLDOMDocument::insertBefore()

I am using MSXML to generate an XML document.  I use the loadXML method to generate the DOCTYPE node and then need to add the processing instruction above the DocType.  I am trying to use insertBefore to do it, but can't seem to get the refChild argument right.  Could someone give me a hand?  I guess I am not sure in what format the pointer to the IXMLDOMNode is supposed to be assigned to a VARIANT.  This was my best guess, but it always fails at the insertBefore call.  Below is the code:

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    //Create DocType Reference
    hr = pDoc->loadXML(L"<!DOCTYPE Test SYSTEM \"Test.dtd\">\n<Test></Test>", &varResult);
    if(hr!=S_OK || varResult!=VARIANT_TRUE){
        if(pDoc->get_parseError(&pXMLErr)==S_OK){
            if(node.Import(pXMLErr)){
                strError.Format("Unable to build XML file.  %s.", node.text);
                throw strError;
            }
            pXMLErr->Release();
            pXMLErr=NULL;
        }
        strError = "Unable to build XML file.  The file may be reserved by the operating system.";
        throw strError;
    }

    if(pDoc->get_childNodes(&pNodes)!=S_OK){
        strError = "Unable to create root element.";
        throw strError;
    }

    //Create Processing Instruction
    if(pNodes->get_item(0, &pDocType)!=S_OK){
        strError = "Unable to create root element.";
        throw strError;
    }
    VariantInit(&varRefChild);
    varRefChild.vt = VT_UI4;
    varRefChild.uiVal = (unsigned int) pDocType;
    if(pDoc->createProcessingInstruction(L"xml", L"version=\"1.0\" encoding=\"UTF-8\"", &pProcessInstruction)!=S_OK){
        strError = "Unable to create xml processing instruction.";
        throw strError;
    }
    if(pDoc->insertBefore(pProcessInstruction, varRefChild, &pNode)!=S_OK){
        strError = "Unable to add xml processing instruction.";
        throw strError;
    }
    pDocType.Release();
    pNode.Release();
    pProcessInstruction.Release();
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Thanks,
David Johns