Good eyes!
That decal is from the original owner, a bike pass from the University of Oregon that expires 9/30/05. On that date I would have been 6 years old. Crazy.
And thanks to all you others for the help, I'll get out my wrenches and see how much damage I can do.
My (very uneducated) guess is that there is a spring and possible a bolt missing. Near the top spinny-sprocket thingy there is an empty whole, and there just isn't any empty holes on the rest of the derailleur, so add that to all your guys' advice, and I think I found the culprit.
So if there is something missing, what next? Do you think there's still parts around and someone with the loooonng memory to fix it? What about replacing the derailleur. I'm so hung up on the the Peugeot package that I wouldn't want to replace it with un-authentic parts. What's the chance of getting a brand-correct part on the darn thing?
Thanks, you all, for the help, I'd be scratching my head for weeks if it weren't for your advice.