I'd probably suggest running OS 9 over 10.3. That shiznet is old, dude. (And not in a "great, it's now retro!" way; more of a "Really, you expect me to use Windows ME?!?" vibe.) I guess the real question, of course, is what you plan to do with the things. If you're going to try surfing the Internet with them I'd say, uhm... Debian Linux, maybe? NetBSD? *That's* a tough one.