As has been commented your references to namespaces are a red herring.
It's not the different namespaces but the different document that is the
issue.
key() looks up keys in the current document only. If you are in another
document you need to go back to where you want to do the key lookup.
usual model is:
<xsl:variable name="originaldoc" select="/"/>
<xsl:for-each select="document('jhcgalshgalal')/a/b/c">
stuff in other doc...
<xsl:variable select="some expression to generate the key" name="x"/>
<xsl:for-each select="$originaldoc">
<xsl:value-of select="key('k',$x)">
</xsl:for-each>
more stuff in other doc
...
David
XSL-List info and archive: http://www.mulberrytech.com/xsl/xsl-list