Eigen2:

wget http://bitbucket.org/eigen/eigen/get/2.0.17.tar.gz

tar zxvf 2.0.17.tar.gz
mkdir build_eigen
cd build_eigen
cmake ../eigen-eigen-b23437e61a07/ -DCMAKE_INSTALL_PREFIX=/opt/sw/eigen/2.0.17
make install

Openbabel:

wget http://downloads.sourceforge.net/project/openbabel/openbabel/2.3.1/openbabel-2.3.1.tar.gz
tar zxvf openbabel-2.3.1.tar.gz
mkdir build
cd build

cmake ../openbabel-2.3.1 -DCMAKE_INSTALL_PREFIX=/opt/sw/openbabel/2.3.1  \
-DPYTHON_EXECUTABLE:FILEPATH=/usr/bin/python2.4 \
-DBUILD_GUI=OFF -DPYTHON_BINDINGS=ON -DEIGEN2_INCLUDE_DIR=/opt/sw/eigen/2.0.17/include/eigen2/

make 
make install

update PYTHONPATH and LD_LIBRARY_PATH in ~/.bashrc:

export LD_LIBRARY_PATH=/opt/sw/openbabel/2.3.1/lib:$LD_LIBRARY_PATH
export PYTHONPATH=/opt/sw/openbabel/2.3.1/lib64/python2.4/site-packages:$PYTHONPATH

python usage:

$ python
Python 2.4.3 (#1, Nov 11 2010, 13:30:19) 
[GCC 4.1.2 20080704 (Red Hat 4.1.2-48)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import openbabel
>>>