_WIN64
can be used to find the platform to be 32-bit or 64-bit.
Are there any macros available in drivers (kernel mode code) that can be used to tell the version of the operating system. XP, 2003, Vista or 7?
The info you need is here. Check out SdkDdkVer.h
in your build environment. Especially useful: NTDDI_VERSION.