How Can I Load a Genuine Windows XP Servicepack 3 Over a Fake Windows XP on My PC

If you already have a legitimate version of XP with a legitimate key, you may follow these directions to change your XP key and not have to reload anything. (Note : You must have a legal copy and key from Microsoft.)

http://pcsupport.about.com/od/productkeysactivation/ht/changexpkey.htm

J pool, Will this hange of key affect any files or folders already in the PC ?

No Sir, will change nothing but the Windows Key from the pirated one to your legit one. Follow instructions carefully, print them out first, you are editing the registry.

I had bought a Pentium III Laptop a few years ago off of e-bay, and it had a pirated copy of XP on it. I bought a new copy of XP, and did this instead of reloading XP and all the drivers.