Apart from the MSDN reference, I want to know what these keys do? Does KEY_WOW64_32KEY means that a 32-bit app on x64 OS will access the WOW64 Registry Tree ? And does KEY_WOW64_64KEY means that a 32-bit app on x64 OS will access the normal Registry Tree and not the WOW64 Registry Tree ? What if I have to access some keys which I do not know whether lies in the WOW64 or normal Registry Tree ?
KEY_WOW64_64KEY on a 64-bit OS means that the registry access, no matter if it's a 32 or 64 bit process, will access the 64 bit registry view.
KEY_WOW64_32KEY on a 64-bit OS means that the registry access, no matter if it's a 32 or 64 bit process, will access the 32 bit registry view.
Neither of them have any effect on a 32-bit OS.
Leaving the flag out (the default) on a 64-bit OS will send registry accesses from 32-bit processes to the 32 bit registry view, and accesses from 64-bit processes to the 64 bit registry view.
For more info, this reference page at Microsoft should tell the whole tale.