Here's out ant task which runs fine from Eclipse under Hibernate 3.1.2
Code:
<target name="hbm2java" description="Generate .java from .hbm files.">
<delete>
<fileset dir="${hibernateDO.dir}">
<include name="**/*.java"/>
</fileset>
</delete>
<taskdef name="hibernatetool" classname="org.hibernate.tool.ant.HibernateToolTask">
<classpath refid="classpath.common"/>
</taskdef>
<hibernatetool destdir="${src.dir}">
<configuration>
<fileset dir="${src.dir}">
<include name="**/hbm/*.hbm.xml"/>
</fileset>
</configuration>
<hbm2java generics="false"/>
</hibernatetool>
</target>
Don't forget to rate if this helps :-)