Re: and yet another way to do it. . .
Man, is that ever complicated! As far as just recording the ID, I think Justin nailed it with his encryption idea. What you're describing gets into another area: Having the server recognize you and tag you with a permanent ID. We could do that with a membership system that uses traditional login or digital certificates; or use voluntary cookies to remember your name and optional email address to supply in message forms. Those techniques would be a little easier, and would have some other benefits.
(knows very little about programming a BBS, glad Justin and Robert do)
It's a dirty job, but somebody's gotta do it....
--Robert