i use opengl 2.1.1 on linux with freeglut 2.4.0. the new enums are not to be found in my freeglut_std.h along with the other ones, which makes it kind of odd that they work for me. sdl uses buttons 4 and 5 as wheel-up/down, too, which is why i tried this in the first place. they seem not to be "officially" supported on windows either as there is a patch for a windows port of glut to make it mousewheel-aware at all at http://www.realmtech.net/opengl/glut.php , providing the very same enums.
This is interesting. Are you sure your system is configured to use freeglut? I ask only because the windows glut you link to is definitely not freeglut. My freeglut-2.4.0 provides a libglut-3.8.0.so lib file. Second are you using cl-opengl-thomas? I queried my mice with xinput and the wheel is mapped to buttons 4 and 5 however my system only provides the enums in the freeglut headers
charlie mac