Ah -- I see. This DataSet is coming from a .NET service (probably generated by ADO.NET), and then stuffed into the SOAP message as a string. Unfortunately, because the string starts with the <?xml> declaration, you won't be able to get Axis to process it for you. You are going to have to extract the string and then process it using SAX or DOM.
You need to go abuse the card processing folks. This is what's known as a "worst practice". Anne