I think Carol is right .. A typical directory structure would be
jsp WEB-INF
lib
classes
web.xml
If this is similar to your directory structure then the jars are getting added twice because you have <lib> and <webinf> defined in your build.xml.
You may want to change your war task to
<war destfile="${build.dir}/${deploy.name}" webxml="WEB-INF/web.xml">
<fileset dir="${jsp.dir}" includes="**\*"/>
<metainf dir="META-INF"/>
<webinf dir="WEB-INF\">
<exclude name="web2.xml"/>
<exclude name="web.xml"/>
<exclude name="**\j2ee.jar"/>
</webinf>
</war>
[ January 14, 2005: Message edited by: Amber Vaidya ]