download a tarball of 0.20.204.0, untar and do "ant eclipse": it will fail with the following error message:
The fix seems simple - just pre-create .eclipse.templates directory.
[eclipse] There were no settings found.
[eclipse] Writing the project definition in the mode "java".
[eclipse] Writing the classpath definition.
/private/tmp/hadoop-0.20.204.0/build.xml:2245: /private/tmp/hadoop-0.20.204.0/.eclipse.templates does not exist.