Apparently Nirsoft's ProduKey can do this:
produkey.exe /windir [Windows Directory]
Load product key information from
another operating system on the same
computer. The [Windows Directory]
specifies the base folder of Windows
installation, for example: c:\windows,
c:\winnt This feature is only
supported on Windows
2000/XP/2003/2008/Vista/7.
If that doesn't work, you'll have to dig it out of the registry file manually by searching
C:\WINDOWS\system32\config\software
for the registry key
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\DigitalProductId
using a hex editor I think.
Bytes 52-66 (0x34 - 0x42) of this key hold a 15 byte number.
In Hex, it's a 30 digit number:
A2 23 51 D0 2A 38 5D 22 C4 41 6B 87 43 C1 00
In Binary, a 120 digit number:
10100010 00100011 ... 11000001 00000000
Converted to base 24:
751AA001EHCCLAB3JH8KDIGAG
Mapped to Microsoft's custom base24 alphabet "BCDFGHJKMPQRTVWXY2346789" and a hyphen every 5 chars:
KHCQQ-BBCW2-TT7QR-F42M6-V3YQY
I did it this way about 4 years ago, so I'm really hoping ProduKey works.
Keep in mind that most OEM XP and up license key stickers were special numbers to begin with. You can't usually reinstall with that number, and I believe the number in the registry reflects the number on the case. – Paul McMillan – 2009-08-30T15:06:13.350
1Note that Fortyrunner has said that the registry is on ANOTHER disk from another computer. Using Jellybean/WinKeyFinder/KeyFinder as suggested will not work in this instance. – Kez – 2009-08-30T17:19:46.013
and why would winkeyfinder not work? connect the HDD to any computer (to be sure, remove all other HDDs), now boot from a windows XP CDROM and run a repair installation, then retrieve your license keys with winkeyfinder. walk in the park. – None – 2009-08-30T21:02:28.857