namespace and schema reference issues

Well I  have just another (hope so) easy to answer question.
If I load an XML instance, which has a schema reference and a default namespace attached to it, into my xform document, how should the namespace and the refernce to treated? It seems like that the schema reference is not always needed because it could be already declared in the xform:schema element. Or am I something missing? 
The problem with the default namespace is that we have tried to navigated through our Xform document with XPath, but MSXML was unfortunately not able to do that properly (although the syntax was definitely rigth ;) ).
I hope you can help me :)
 
wbr, 
Roman Huditsch