Thanks. I searched winehq database but didn't find anything appropriate.

LicenseCrawler works under wine or in a VM accurately. Note that in Wine, it will search the Wine registry. You'll probably have to use regedit to export your windows registry and load it into Wine, probably trashing wine's setup to get the program to read the Windows registry. Haven't tried that yet but see no reason why it wouldn't work. I'll let you know...

I found the following instructions on the net that produced some sort of Product Key using a Linux based CD with a rudimentary registry editor and a Windows application KeyViewer. However my PC would not accept this Product Key as a correct one. I then ran KeyViewer on another XP system with a known Product Key and it produced an incorrect one again. I am going to copy the instructions here anyway, it's possible that keyviewer works only for certain versions of XP - Home/Professional, OEM/non-OEM etc or that another segment of XP registry has to be inspected.

Create bootdisk from the cd050303.iso
found here: http://home.eunet.no/~pnordahl/ntpasswd/

Boot (dead) system using the bootdisk (CD)
*Note: BIOS must be set to boot from CD

1. Select disk where the windows installation is located. Generally this would be the first one listed (is also notated by Boot). Press '1' [Enter] to select the first drive listed.

2a) Enter path to the registry files. (Press [Enter] to select default)

2b) Select which part of the registry to edit. In this case, you want 'software' so type: software [Enter]

3. You should now see the loaded hives indicates <software>
Select '9' [Enter]
At prompt, do the following:
Type: cd Microsoft\Windows NT\CurrentVersion [Enter]
Type: hex DigitalProductId [Enter]

This will list the value of the DigitalProductId. Look for the line 0030.
Starting from the 5th column (following 00 00 00 00) write down the next
15x HEX code values (each set of 2 characters is a hex value).
You should end up with 30 characters, ending on the row beginning with
0040, in the 3rd column.

Eg. 7F6A514C8E5A9156EA34771AB7F202
Now that you have what you need, you can either just eject your CD and
shut down the dead PC, or shut down properly by typing:
q [Enter]
q [Enter]
n [Enter]
exit [Enter] (then wait for prompt)
Eject CD and shut down.

From either a boot floppy also containing the key viewer, or from a working system,
run KeyViewer which can be downloaded from here:
http://www.ac2tech.com/tools/keyviewer/keyviewer.php

Select the tab, 'Raw Key'.
Enter in the 30 character Hex code you wrote down (no spaces) and press the
Decode button. The Product Key will appear in the window below.

Well, that's interesting. I have to say, using Keyviewer or LicenseCrawler on my home machine gives the same ProductID/Serial number as on the outside label, as it should.

All the work machines don't match their stickers. I don't know if that's by design (randomly install different versions on machines than their labels as some kind of misguided security), because of corporate licensing and the Windows versions, roaming profiles, because of sloppy cloning and installation (most likely) or what.

I tested KeyViewer on an XP home edition w/s that I (re)installed myself from its native Product Key. The product key that KeyFinder gave me for it upon launching looked nothing like the key on the box.