Which WinXP version is it that you can use multiple CD Keys on? I've got WinXP Home on my computer right now, and my stepbrother gave me his WinXP Pro CD / Key, but I'm not sure if I could use it or not. I could have sworn that both Home and Pro versions check back with a central server, or something somewhere, to check to see if the Product ID # / Key has already been used. Or, is it just Home that uses the 'authorization'? Reason I'm asking, is I'm thinking of upgrading to XP Pro, as well as formatting my main drive, and he just gave me the CD and told me to 'use this', as he no longer needs it. So. Would it matter, or not, if he has already used the CD Key on it, or not? I'm willing to go out and buy a version of it if it's already used, just curious.