Okay, people, thanks to fellow poster RogerS, I managed to install Python 2.5 on my N800. Here's what I did:

I went to the Python page: http://pymaemo.garage.maemo.org/ and clicked on the link to the Bora installer (assuming everyone in this thread has a N800), but instead of installing, I clicked on "save" and saved the installation file on my memory card.

I then did a lot of superfluous things, but the thing you should do, is go into the Application Manager and delete the "bora-extras" repository (http://catalogue.tableteer.nokia.com/certified/ bora user) from the catalogue list (that is, if you have that repository in your list).

Next, open the file manager and find the installation file (hopefully you didn't bury it way deep into the directory tree), "python2.5-runtime", and double-click it. The application manager will ask you if it can add the bora-extras repository; say "yes". If all goes as it went here, you should get the standard application installation dialogs from now on, ending with the near-climactic finale of your N800 telling you that Python 2.5 is now installed.