If you have the COA sticker affixed to the computer just get a copy of the proper media. M$ sells it for about 25 bucks but chances are somebody you know has a copy. The media is the same fr every version ie Home, Pro etc, it is the unique key you need. You can also extract the CD key if for some reason you do not have the COA sticker. Use a program called PRODUKEY. It is a free download. Just download it, run it and write down the CD key and you can use it to reinstall your OS. There is also a program called Aida32 that will display your CD key and it is also free. Might want to bump the RAM up at the same time as Windows XP with SP3 uses a lot more memory.