I just wanted to know the API to get information about product key / serial key of Windows Guest OS running as Virtual Machine?
(1) You can get it from the registry: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\ProductId
(2) Or you can get it via WMI. http://msdn.microsoft.com/en-us/library/cc534596(VS.85).aspx
See this VBS as an example:
It is in your %SYSTEM32% directory.
Hope this will help,