ROS installation on Mac with Homebrew--bootstrapping issues?

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Hi!

I'm trying to install ROS on my MacBook Pro (running Mac OS X 10.7.3). I have followed everything in the installation instructions here (http://www.ros.org/wiki/electric/Installation/OSX/Homebrew), but at the very end of the Desktop-Full Install, I get this:

(Over-)Writing setup.sh, setup.bash, and setup.zsh in /Users/lauraS/ros
Bootstrapping ROS build
Detected ros_comm bootstrapping it too.
sed: illegal option -- s
usage: sed script [-Ealn] [-i extension] [file ...]
       sed [-Ealn] [-i extension] [-e script] ... [-f script_file] ... [file ...]
sed: illegal option -- s
usage: sed script [-Ealn] [-i extension] [file ...]
       sed [-Ealn] [-i extension] [-e script] ... [-f script_file] ... [file ...]
sed: illegal option -- s
usage: sed script [-Ealn] [-i extension] [file ...]
       sed [-Ealn] [-i extension] [-e script] ... [-f script_file] ... [file ...]
/bin/bash: rosmake: command not found
Traceback (most recent call last):
  File "/usr/local/bin/rosinstall", line 5, in <module>
    pkg_resources.run_script('rosinstall==0.6.11', 'rosinstall')
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/pkg_resources.py", line 489, in run_script
    self.require(requires)[0].run_script(script_name, ns)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/pkg_resources.py", line 1214, in run_script
    exec script_code in namespace, namespace
  File "/Library/Python/2.7/site-packages/rosinstall-0.6.11-py2.7.egg/EGG-INFO/scripts/rosinstall", line 11, in <module>

  File "build/bdist.macosx-10.7-intel/egg/rosinstall/rosinstall_cli.py", line 213, in rosinstall_main
  File "build/bdist.macosx-10.7-intel/egg/rosinstall/rosinstall_cmd.py", line 88, in cmd_generate_ros_files
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/subprocess.py", line 504, in check_call
    raise CalledProcessError(retcode, cmd)
subprocess.CalledProcessError: Command 'source /Users/lauraS/ros/setup.sh && rosmake ros ros_comm --rosdep-install' returned non-zero exit status 127

And if I try to run the next step, source ~/ros/setup.bash, I get:

    sed: illegal option -- s
usage: sed script [-Ealn] [-i extension] [file ...]
       sed [-Ealn] [-i extension] [-e script] ... [-f script_file] ... [file ...]
sed: illegal option -- s
usage: sed script [-Ealn] [-i extension] [file ...]
       sed [-Ealn] [-i extension] [-e script] ... [-f script_file] ... [file ...]
sed: illegal option -- s
usage: sed script [-Ealn] [-i extension] [file ...]
       sed [-Ealn] [-i extension] [-e script] ... [-f script_file] ... [file ...]
rospack could not be found, you cannot have rosbash features until you bootstrap ros

I'm kind of new at this and am not actually sure what bootstrapping is, and I've no idea how to go about getting things installed properly from this point. Any help would be appreciated! Thanks!

Update: After taking tmf's suggestions, I think the installer has gotten further than it got before, but now after rosinstall installs robot_model_tutorials, I get this:

(Over-)Writing setup.sh, setup.bash, and setup.zsh in /Users/lauraS/ros
Bootstrapping ROS build
Detected ros_comm bootstrapping it too.

and then it hangs until I ctrl-c it. For the record, I have tried running the rosinstall command both on a ~/ros folder that has all of the files from the previous install attempts in it and on a ... (more)