Just purchased a refurbished cpu with XP Pro. It has a COA - do I buy XP Pro or can I use a copy form a friend?

... if it has XP pro... why do you need to buy it? I'm confused.

If it already has XP Pro installed, do you have the License Key? It's usually on a colorful Authenticity Tag on the back or bottom of the computer.

If you have the License Key, then you can make a copy of your friends XP Pro disks, then use your own Key if you ever have to install. Make sure your friend knows you DON'T want his Key.

If you DON'T have the key, run this utility to read the key directly out of your own computer:
Magical Jelly Bean Software - Magical Jelly Bean Keyfinder v2.0.1