Is it possible to install Python 2.5 in 11.04?
Launchpad has a topic about this.
Here is a tutorial on installing python 2.5 on Ubuntu 10.10. 11.04 should be identical for this.
From that websites the commands would be:
sudo add-apt-repository ppa:fkrull/deadsnakes
sudo apt-get update
sudo apt-get install python2.5
Executing python2.5 file
at commandline would execute 'file' with v2.5. python file
would use the newest version.
I only used this once roughly a year ago so be wary of pitfalls.