|You using the Windows Product Key is NOT legal, as far as Microsoft is concerned, unless you ALSO have a genuine Microsoft label to go along with it with a Product Key on it for the same version of Windows as on the hard drive (in this case, XP Pro, Home, MCE 200x, or Pro 64 bit) .|
In the case of a major brand name system computer's original software installation, the Product Key that was originally used is different than the Product Key on the official label stuck to the outside of the same computer's case (, or on the computer case the drive was originally in) - that's normal.
A generic computer is supposed to have the official Microsoft label stuck to the outside of the original case, but sometimes people never installed it there and had it loose. Rarely, they may have installed it inside the case.
Connect the hard drive to a working computer that is running the same "family" of Windows - XP, or Vista, or Windows 7.
Connect it as Slave if it's an IDE drive, or any way as long as you're not booting the computer from it.
Note which drive letter is assigned to the drive, or if it has more than one partition, the drive letter for the partition Windows itself was installed on.
Windows will assign the first drive letter(s) available alphabetically to it's partition(s).
Search for Magic Jelly Bean Keyfinder.
Install and run Keyfinder on the computer that has the non booting hard drive you want to find the Product Key on
At the top, select Tools, then Open Hive
Go to the drive letter of the non booting drive's partition that has Windows itself installed on it that you want the Product Key for, then click on the Windows folder to OPEN it
Keyfinder will find the info on the non booting drive, if the necessary data is still intact.
It will show the Windows version found on the non-booting drive, and which Service Pack it has, if it has one. In this case, XP Pro, Home, MCE 200x, or Pro 64 bit; no SP, or SP1, SP2, or SP3.
It will say "Installed from 'xxx' media"
xxx = OEM - it has an OEM license - most brand name computers, and generic computer installations installed from an OEM disk, have that.
xxx = Fully Packaged Product - it has a Retail license - it was installed from Retail media, or from a "For Windows Genuine Advantage Kit" labelled CD.
xxx = Compliance Checked Product - it has an Upgrade (retail upgrade) license.
xxx = Volume - it has a Volume license - it can be used on more than one computer - if the hard drive didn't come from a business or institutional computer, it's probably NOT a legally obtained Product Key.
It will show the Product Key on the CD Key line.
(It WILL NOT find any Product Key if some software HACK was used to make it not necessary to provide it.)
If in doubt about the Product Key having been legally obtained, search the web with the exact Product Key including the dashes - if you get ANY "hits", it's NOT been legally obtained.
Keyfinder also finds Product Keys for some Microsoft software, and keys or serial numbers for some other software.