when you install the windows xp, it does matter which CD you use. it is ok if the installation program accept the Product KEY. When you activate, compare the key with the sticker, sometimes it is changed. You can activate it after you install. if you can not activate by internet, you will be told to call microsoft to activate it. When you activate it by phone, the other side is an automatic answer machine. if they doubt your copy, someone will talk to you.