Windows 7 Tip: 
If you’ve lost your product key of Windows 7, Vista, XP and Office Product Key, it can be very difficult to recover it if you just look for it at your registry. WinGuggle is a small application that can get your Windows Vista Product Key easily. No Installation is needed, just unzip the archive and launch the application. Therefore, it won’t even take you a long time until you can recover your key.
See Also: Windows 7 RC Activation Product key
See Also: 8 Free Serial Key/Product Key Finder Tools
Features:
· Get Windows Vista and Office Product Key (CD Key)
· Change OEM Logo and Information Completely (Vista and XP)
· Change Performance Information and Tools OEM Logo (Vista Only)
· Manual and Automatic Backup of OEM Logo and Information Settings
· Reset to Default Restore’s the Original Settings
· Your Anti-Virus will not give any alarm message
Download WinGuggle here
I bought a second hand laptop and i changed the user info and backup the serial.
WinGuggle is a basic, no frills program that has only one fundamental function; to find your original product key.
very useful util!