Two errors, the first trivial.
In the Gentoo install wiki 
http://www.ros.org/wiki/fuerte/Installation/Gentoo
It says to "make install" should be "sudo make install"

The second error is more difficult.
When actually doing the install, it does part of it, but then fails at 
catlin
This is the actual end of the install attempt. It was made with

cmake .. -DCMAKE_INSTALL_PREFIX=/opt/ros/fuerte -DSETUPTOOLS_DEB_LAYOUT=OFF

  notice that the error line contains deb stuff.


-- Installing: /opt/ros/fuerte/share/catkin//cmake/test
-- Up-to-date: /opt/ros/fuerte/share/catkin//cmake/test/download_checkmd5.py
-- Up-to-date: /opt/ros/fuerte/share/catkin//cmake/test/runtests.py
-- Up-to-date: /opt/ros/fuerte/share/catkin//cmake/catkin-config.cmake.in
-- Up-to-date: /opt/ros/fuerte/share/catkin//cmake/catkin_project.cmake
-- Installing: /opt/ros/fuerte/share/catkin//cmake/em
-- Up-to-date: 
/opt/ros/fuerte/share/catkin//cmake/em/topologically_traverse.cmake.em
-- Up-to-date: /opt/ros/fuerte/share/catkin//cmake/em/pkg-config.pc.em
-- Up-to-date: /opt/ros/fuerte/share/catkin//cmake/em/manifest.xml.em
-- Up-to-date: /opt/ros/fuerte/share/catkin//cmake/all.cmake
-- Up-to-date: 
/opt/ros/fuerte/share/catkin//cmake/check_unused_arguments.cmake
-- Up-to-date: /opt/ros/fuerte/share/catkin/cmake/tests.cmake
+ '[' -n '' ']'
+ cd /home/chris/ros-underlay/catkin
+ /usr/bin/env 
PYTHONPATH=/opt/ros/fuerte/lib/python2.7/dist-packages:/home/chris/ros-underlay/build/gen/py 
CATKIN_BINARY_DIR=/home/chris/ros-underlay/build /usr/bin/python 
/home/chris/ros-underlay/catkin/setup.py install --install-layout=deb 
--prefix=/opt/ros/fuerte
usage: setup.py [global_opts] cmd1 [cmd1_opts] [cmd2 [cmd2_opts] ...]
    or: setup.py --help [cmd1 cmd2 ...]
    or: setup.py --help-commands
    or: setup.py cmd --help

error: option --install-layout not recognized
CMake Error at catkin/CMakeFiles/safe_execute_install.cmake:5 (message):
   Error executing process with arguments
Call Stack (most recent call first):
   catkin/cmake_install.cmake:119 (INCLUDE)
   cmake_install.cmake:37 (INCLUDE)


make: *** [install] Error 1

-- 
Chris Bruner