I''ve downloaded some OpenGL examples in c, and when I compile these Visual C++ 6 gives a list of errors in OpenGL.h. But when I use it in a C++-file, it doesn''t give problems at all. Why? May Eru Ilúvator and the Valar be with you!

I don''t know which demos you downloaded, but OpenGL.h isn''t a standard GL header file. My guess is that OpenGL.h had some C++ specific code that the C compiler barfed on. The OpenGL header that ships with Visual C++ is Gl.h, which is usable from C.