depending on the computer there are several distros that come to mind, have a google for
smoothwall
ipcop
lrp
there are are more, but, off the top of my head i can't remember. the different distros have different system requirements, so that will be something to look at for the box in question. hope theres something here that can help you, or answer your questions.
good luck.
<edit>beat to the draw by the Tinkster, what can i say, glad we're playing for the same team.

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<double edit> that was surreal, the first time i was taken to the post, Tinkster was the first response, in retrospect, we were both beaten to the draw, wow what fun.

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