Useful guide to install python 2.5 on Ubuntu 10.04

sudo apt-get update
sudo apt-get install build-essential gcc


cd Downloads
wget http://www.python.org/ftp/python/2.5.6/Python-2.5.6.tgz
tar -xvzf Python-2.5.6.tgz
cd Python-2.5.6
./configure --prefix=/usr/local/python2.5
make
make test
sudo make install
sudo ln -s /usr/local/python2.5/bin/python /usr/bin/python2.5 


Reference:
http://welcometoubuntu.blogspot.com/2010/05/howto-install-python-255-on-ubuntu-1004.html