You'll have to do something like this:
IXMLDOMNode newField = blabla.cloneNode( false );
newField.text = "xxx";
IXMLDOMNode groupNode = thisXDocument.dom.selectSingleNode( "XPath/to/containingGroupNode" );
groupeNode.appendChild( newField );
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Matt Faus
InfoPath Dev Texas
Matt Faus / Microsoft InfoPath MVPQdabra® Software / Streamline data gathering to turn process into knowledge