The <taglib> element is a sub element of <jsp-config>, thus it should be:
<jsp-config>
<taglib>
<taglib-uri>
http://displaytag.sf.net</taglib-uri>
<taglib-location>/WEB-INF/displaytag-el.tld</taglib-location>
</taglib>
</jsp-config>
--
Wolfram Rittmeyer