This is the firs time I have to work with a WFS (I have to connect my app to a WFS in ArcGIS server) and I found the IWFSServer Interface. I use this code to get the capabilities xml:
<ows:ExceptionReport version='1.1.0' language='en' xmlns:ows='http://www.opengis.net/ows'><ows:Exception exceptionCode='NoApplicableCode'><ows:ExceptionText>Xml Parsing failed. Reason:Invalid at the top level of the document.