help on install ROS in a MacBook with OSX 10.6.6

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I am trying to install ROS in my MacBook OSX 10.6.6.

after doing the command: rosinstall ~/ros "http://packages.ros.org/cgi-bin/gen_rosinstall.py?rosdistro=diamondback&variant=ros-full&overlay=no"

that appears in "http://www.ros.org/wiki/diamondback/Installation/OSX".

I got this output, can anyone give a hint how to solve this issue? ...

Bootstrapping ROS build
Detected ros_comm bootstrapping it too.
Traceback (most recent call last):
  File "/Users/paulogoncalves/ros/ros/bin/rosmake", line 60, in <module>
    from ros import rosmake
  File "/Users/paulogoncalves/ros/ros/core/roslib/src/ros/__init__.py", line 41, in <module>
    import roslib
  File "/Users/paulogoncalves/ros/ros/core/roslib/src/roslib/__init__.py", line 50, in <module>
    from roslib.launcher import load_manifest
  File "/Users/paulogoncalves/ros/ros/core/roslib/src/roslib/launcher.py", line 45, in <module>
    import roslib.manifest
  File "/Users/paulogoncalves/ros/ros/core/roslib/src/roslib/manifest.py", line 46, in <module>
    import roslib.packages
  File "/Users/paulogoncalves/ros/ros/core/roslib/src/roslib/packages.py", line 58, in <module>
    import roslib.os_detect
  File "/Users/paulogoncalves/ros/ros/core/roslib/src/roslib/os_detect.py", line 49, in <module>
    import yaml
ImportError: No module named yaml
Traceback (most recent call last):
  File "/usr/local/bin/rosinstall", line 5, in <module>
    pkg_resources.run_script('rosinstall==0.5.16', 'rosinstall')
  File "/System/Library/Frameworks/Python.framework/Versions/2.6/Extras/lib/python/pkg_resources.py", line 442, in run_script
    self.require(requires)[0].run_script(script_name, ns)
  File "/System/Library/Frameworks/Python.framework/Versions/2.6/Extras/lib/python/pkg_resources.py", line 1167, in run_script
    exec script_code in namespace, namespace
  File "/Library/Python/2.6/site-packages/rosinstall-0.5.16-py2.6.egg/EGG-INFO/scripts/rosinstall", line 556, in <module>

  File "/Library/Python/2.6/site-packages/rosinstall-0.5.16-py2.6.egg/EGG-INFO/scripts/rosinstall", line 547, in rosinstall_main

  File "/System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/subprocess.py", line 462, in check_call
    raise CalledProcessError(retcode, cmd)
subprocess.CalledProcessError: Command 'source /Users/paulogoncalves/ros/setup.sh && rosmake ros ros_comm --rosdep-install' returned non-zero exit status 1

thx, Paulo.