Can't create namespaces attributes...

[ds...@mmm.com]

I would like to create the following document
<request xmlns="http://somedefaultnamespace" xmlns:test
="http://secondnamespace">
     <value>100</value>
     <test:value>150</test:value>
</request>

Whenever I try to add a namespace attribute with the format xmlns:test I
get an error.  I CAN create namespaces via the
root.setAttributeNS("http://x.com/ns","x:hi","myvalue");
OR
Attr myattr = mydoc.createAttributeNS("http://someuri","myname");

It appears these namespace(s) are visible within the Xerces object classes
(tested through the root.getAttributeNodeNS("http://x.com/ns","hi")) method
and it returns the correct node...however if I write this XML document out
(to a string or a file) I do not see the xmlns attributes like I would
expect to see....
Any ideas??  Am I not calling the right method?  Why isn't there a
createnamespace method?

thanks
Doug