Default namespace in XML document

I have an XML document with a default namespace indicated at the root.
Something like this:

<MyRoot xmlns="http://www.mysite.com">
<!-- a lotta XML in here -->
</MyRoot>

My XSLT to parse the XML does not work as expected because of the
default namespace, i.e. when I remove the namespace, everyting works as
expected. All XPATH statements find their intended values. Since I don't
have control over the source XML and the included default namespace,
what should I do to my XSLT so that my XPATH expressions find their
intended values?

BTW: I'm using the XERCES parser.

Thanks,

Kevin