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making a linux os
er… do you mean something like finding a collection of components you can put together to make a functional os? I'm no pro there but I'd say all you'd really need to do would be to download a kernel, a shell, and some programs. That's essentially what Linux is, at the simplest level, or any OS for that matter. I've heard of this before in Popular Science magazine, but not sure exactly how you'd go about doing it. Good luck anyway…
But, if you want a small bootable linux distro, I'd go with DamnSmallLinux, Gentoo Minimal, or Xubuntu. They'd fit very well on a flash drive and, because they're so small, could be loaded completely into ram.