XPath help

I want to create a view of my data and hold it in a global variable,
something like this (which does not work):
<xsl:variable name="leftnav.imagenodes"
select="/page/globalnav[@id='leftnav']//navimg"/>
<!-- note: there is a topnav and rightnav, so those would eventually go into
a global "view" variable -->

I don't seem to be gathering any nodes...

The XML looks something like this (snipped out unnecessary tags):
<page lang="en">
  <globalnav id="leftnav">
   <navimg id="joinus" filename="/but_joinus.gif" lang="en"/>
   <navimg id="joinus" filename="/spanish/but_joinus.gif" lang="es"/>
   <section>
      <navimg id="discover" filename="/but_discover_off.gif" lang="en"/>
      <navimg id="discover" filename="/but_discover_off.gif" lang="es"/>
   </section>
  </globalnav>
</page>

What would the correct XPath expression be if I wanted to hold all the
navimg's in a variable so I can access by doing something like this from any
template:
<img src="&img_uri;/{$leftnav.imagenodes[@id='joinus'and
@lang=/page/@lang]}"/>


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