Find a lost Windows product key
For older versions of Windows you can extract the product key from the Windows Registry. Click Start | Run and then type regedit and click OK.
For Windows 95 and Windows 98, browse to this key:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\ProductID
For Windows NT 4.0, browse to this key:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\ProductID