Do I need to register my Windows?

Hello
I have a Dell P4 desktop which I got it from my friend. I want to use it for my store at work, I want to know if there is need for registerring it with Microsoft the windows is install a OEM version XP. The product sticker is on the side of the box, and I used the key when I installed the windows. I dont know this computer who got it first, he registred or not with Microsoft?

Thanks