website: Accessing the value of config elements

Hello,

I am trying to access the value of a config element within the template 
allpagesbanner but without success.

My webpage dokument looks at the top like this:

<webpage id="de.dialog.beirat" lang="de">
   <config param="contentgroup" value="deutschland"/>

My templates looks like this:

<div id="allpagesbanner">
  <xsl:variable name="contentgroup"
     select="/webpage/config[@param='contentgroup']" />
...

How can I access the config element I need in XSL?

Regards,

Oliver