soap body creation error

OK, no matter how hard I try I cannot figure the way this works... there is a certain magic attached to all SOAP related object that I cannot really understand...

I want to create the following with the PHP SOAP classes SoapClient, SoapParam etc...

Please help me understand how to do it. I created a somehow complex XML structure so that I can really "get" what is going on...

<env:Envelope>
  <env:Body>
    <ns:myMethod> 
        <TheInput xsi:type="ns:TheInputUser"> 
            <ns:username>XXXX</ns:username> 
        </TheInput> 
        <TheOutput xsi:type="ns:TheOutUser"> 
            <ns:var xsi:nil="true"/> 
        </TheOutput> 
        <Array1 xsi:type="ns:UserArray1"/> 
        <IdOut xsi:type="xsd:decimal">0</IdOut> 
        <ErrorOut xsi:type="ns:ErrorUser"> 
            <ns:errorDescr xsi:nil="true"/> 
        </ErrorOut> 
    </ns:myMethod> 
  </env:Body> 
</env:Envelope> 

thanks in advance