gistfile1.txt

$ virtualenv --no-site-packages -p `which python2.5` test-2.5
Running virtualenv with interpreter /usr/bin/python2.5
New python executable in test-2.5/bin/python2.5
Also creating executable in test-2.5/bin/python
Installing setuptools......................
  Complete output from command test-2.5/bin/python2.5 -c "#!python
\"\"\"Bootstrap setuptoo...




" /usr/lib/python2.6/dist-packag...5.egg:
  Downloading http://pypi.python.org/packages/2.5/s/setuptools/setuptools-0.6c9-py2.5.egg
Traceback (most recent call last):
  File "<string>", line 270, in <module>
  File "<string>", line 204, in main
  File "build/bdist.linux-i686/egg/setuptools/__init__.py", line 2, in <module>
  File "build/bdist.linux-i686/egg/setuptools/extension.py", line 2, in <module>
  File "build/bdist.linux-i686/egg/setuptools/dist.py", line 6, in <module>
  File "build/bdist.linux-i686/egg/setuptools/command/sdist.py", line 4, in <module>
  File "/usr/lib/python2.5/site-packages/pkg_resources.py", line 2582, in <module>
    add_activation_listener(lambda dist: dist.activate())
  File "/usr/lib/python2.5/site-packages/pkg_resources.py", line 640, in subscribe
    callback(dist)
  File "/usr/lib/python2.5/site-packages/pkg_resources.py", line 2582, in <lambda>
    add_activation_listener(lambda dist: dist.activate())
  File "/usr/lib/python2.5/site-packages/pkg_resources.py", line 2131, in activate
    map(declare_namespace, self._get_metadata('namespace_packages.txt'))
  File "/usr/lib/python2.5/site-packages/pkg_resources.py", line 1735, in declare_namespace
    __import__(parent)
ImportError: No module named enthought

----------------------------------------
...Installing setuptools...done.
Traceback (most recent call last):
  File "/usr/lib/python2.6/dist-packages/virtualenv.py", line 1231, in <module>
    main()
  File "/usr/lib/python2.6/dist-packages/virtualenv.py", line 420, in main
    unzip_setuptools=options.unzip_setuptools)
  File "/usr/lib/python2.6/dist-packages/virtualenv.py", line 507, in create_environment
    install_setuptools(py_executable, unzip=unzip_setuptools)
  File "/usr/lib/python2.6/dist-packages/virtualenv.py", line 295, in install_setuptools
    cwd=cwd)
  File "/usr/lib/python2.6/dist-packages/virtualenv.py", line 481, in call_subprocess
    % (cmd_desc, proc.returncode))
OSError: Command test-2.5/bin/python2.5 -c "#!python
\"\"\"Bootstrap setuptoo...




" /usr/lib/python2.6/dist-packag...5.egg failed with error code 1

I had a similar problem. This can be caused by having libraries in your PYTHONPATH that depend on libraries in the standard system directory. export PYTHONPATH=; virtualenv --no-site-packages test should work.