If you have a valid XP Pro COA attached to your system, and it's a Dell, you're in luck. All you need is a reinstallation disc. These can be obtained on eBay for $15 to $25. All you have to do is boot from CD, let the program run, you will be asked a few simple questions, you'll be asked to remove the CD, it will reboot, it will ask you to reinsert the disc, and it will finish. You won't even have to enter your COA. When you update, everything will be taken care of, including validation. So make sure you're legal before you attempt this.