I've been playing through Marathon 1 AlephOne on Total Carnage. I happened to find a secret save terminal on 'Pfhoraphobia', which is located in the wall directly to your right of your spawnpoint for the level. If you look straight at the 'secret' door (flat textured in green), and count three of those elongated sphere shapes to the right, the third one is really a save term...!!! I would have included screenshot, but I can't get anything to work. :( The term works fine, though -- I've been using it like crazy to get through this highly difficult level...
I tried emailing email@example.com (listed on the page) but got a mailer daemon.