If you are talking about the xml template contained within a datawindow definition you may be able to use a third party tool to generate an XML document from an XSD Schema and then use that.

If you are talking about creating an entire datawindow definition from an XSD Schema you are going to have to manually create it.

I'm not sure that there is a native way to do this, you would have to parse the XSD and create the DW syntax yourself.