XP has a little cool feature called 'undo'. If you have mistakenly copy (how could you do mistake on that?) or PASTE, just hold down CTRL + Z. It will eventually undo from the previous mistake that you have done.
If you kept on undo, then it will automatically undo until it is back to the original source.
If your problem are related to this, then use it
BTW according to your problem, this is more about 'copy it correctly' and 'remember where you got it from'.