The windows API function GetVersionEx, in combination with the info in this article, should tell you everything you need.
BOOL WINAPI GetVersionEx(
__inout LPOSVERSIONINFO lpVersionInfo
);
typedef struct _OSVERSIONINFOEX {
DWORD dwOSVersionInfoSize;
DWORD dwMajorVersion;
DWORD dwMinorVersion;
DWORD dwBuildNumber;
DWORD dwPlatformId;
TCHAR szCSDVersion[128];
WORD wServicePackMajor;
WORD wServicePackMinor;
WORD wSuiteMask;
BYTE wProductType;
BYTE wReserved;
} OSVERSIONINFOEX, *POSVERSIONINFOEX, *LPOSVERSIONINFOEX;