There should be python2.5-runtime in the list of installable packages. Maybe they removed it from the visible list. You could then either enable red-pill-mode (add new catalogue in the application manager, enter "matrix" for location, press cancel, answer popup dialog with "red pill"), use "apt-get install python2.5-runtime" as root, or just install some software which drags in python2.5-runtime as dependency (mediabox, e.g.).