right, there are a couple apps that will pull cd keys...
But, if you are realy interested in the legality of it, just call and ask MS, and if they agree about it ask them if they can supply you with a valid key. if your worried about being busted call from a library or pay phone or something, use a phone card you payed for with cash. As long as the liscence is for a same version of what you have/want installed then I doubt they realy will care a whole lot even though it was still illigal for you have been using it before obtaining the liscence. But I am no laywer. If they get too pissy about it just learn to use linux.
It's not like each cd has it's own key, any cd key will work as long as it's for the same exact version of w2k, you know server for server, professional for professional, student demo version for student demo version, etc etc... If you know somebody with the same version try using their key, if it don't work it don't work, then it's not a big loss... But of course the correct thing to do is contact MS itself.