de-rusting a copper pot?
When you say "rusted," do you mean that there's green copper oxide formed on the outside of the pot, or just that it's really tarnished. If the former, you may need to use some steel wool or other real abrasives to get down to metal that will take a polish. If the later, your job is easier; it just takes time and elbow grease and some good copper cleaner.
The inside is tougher. Assume if it's old, it's tin lined? How does the lining look? If it's corroded through or otherwise in bad shape, it should be re tinned before you cook in it, and re-tinning can be expensive. (I keep wanting to try this myself, but I'm not sure what flux to use.)
I found an old copper bowl, pretty badly rusted and stained, that now looks almost as new as my new set of copper bottom pans. Try BKF -- available at your local Safeway store. (Bar Keeper's Friend -- powder like Comet) I only found it 6 weeks ago, and it's now my best kitchen friend. Follow directions and it should take only a few minutes. DON"T scour, rub gently with cloth or sponge. It reaaly works!