rospkg not found in fuerte

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Dear ROS users,

trying to use

rosrun tf view_frames

I get

Traceback (most recent call last):  
  File "/opt/ros/fuerte/stacks/geometry/tf/scripts/view_frames", line 43, in <module>  
    import roslib; roslib.load_manifest(PKG)   
  File "/opt/ros/fuerte/lib/python2.7/dist-packages/roslib/__init__.py", line 50, in <module>  
    from roslib.launcher import load_manifest  
  File "/opt/ros/fuerte/lib/python2.7/dist-packages/roslib/launcher.py", line 42, in <module>  
    import rospkg  
ImportError: No module named rospkg

...but I cannot find any errors around my environmental variables.. :(