Kwame,
Here is mine. It works perfectly.
<target name="web.compile" depends="init">
<java fork="true" maxmemory="256M" classname="com.google.gwt.dev.GWTCompiler">
<classpath>
<pathelement path="${src.dir}"></pathelement>
<pathelement location="${GWT_HOME}/gwt-user.jar"></pathelement>
<pathelement location="${GWT_HOME}/gwt-dev-linux.jar"></pathelement>
</classpath>
<arg value="-out"/><arg value="www"/>
<arg value="com.mycompany.myapp"/>
</java>
</target>