Windows Xp Key Retrieve Grab The Windows XP Key Off A HD?

Grab the Windows XP Key off a HD? - windows xp key retrieve

I have a computer in the trash and took a few games, I thought I could use. I have the hard drive, and I saw that XP is installed. How do I get the key to the computer? I have an installation CD, but you need the key to format the hard drive and install it on another computer.