回複：再請教：兩年前買的正版WindowsXP，現在重新安裝一下電腦，結果不知為什麽，原光盤還在，但不知把安裝碼弄哪裏去了，請問

Yes, you do if you purchase the OS separate from your PC. If the OS comes with your PC, like DELL, HP etc, there should be a product key on your PC and you don't even have to use this key if you reload the OS with the OS CD provided by them.