Reinstall window XP

I just installed a new HD on my laptop and received a Windows XP from a friend. I installed the Window XP and when the window appeared to input
the Authenticity ID it was missing. How can I delete Windows XP so I can
reinstall another CD with the Authenticity. I tried the new CD but it will not overide the old Window XP. Can anyone Help.

Thanks
Rob

I tried your instructions and it did not work. How can I reformat the HD?

Funny, my instructions are the same as Microsoft's.

http://support.microsoft.com/?kbid=316941

Method 1: Perform a clean install of Windows XP

To perform a clean installation of Windows XP, follow these steps:
Back up all important information before you perform a clean installation of Windows XP. Save the backup to an external location, such as a CD or external hard disk.
Start your computer from the Windows XP CD. To do this, insert the Windows XP CD into your CD drive or DVD drive, and then restart your computer.

Note To boot from your Windows XP CD, the BIOS settings on your computer must be configured to do this.
When you see the "Press any key to boot from CD" message, press any key to start the computer from the Windows XP CD.
At the Welcome to Setup screen, press ENTER to start Windows XP Setup.
Read the Microsoft Software License Terms, and then press F8.
Follow the instructions on the screen to select and format a partition where you want to install Windows XP.
Follow the instructions on the screen to complete the Windows XP Setup.


If you have successfully installed Windows XP, you are finished. If these steps did not help you install Windows XP, go to the "Next Steps" section.