A simple, quick way to find out where a macro has been defined is to redefine the macro and check compiler’s Warning/Error message.
#include <windows.h>
#define min(a,b) nonsense
mintest.cpp(3) : warning C4005: 'min' : macro redefinition
C:\Programme\Microsoft SDKs\Windows\v6.0A\include\windef.h(194) : see previous definition of 'min'