I am a bit annoyed by the zillion versions of glext.h header files floating around OpenGL developer sites. For example, I have compared the one from opengl.org, nvidia.com, and oss.sgi.com. The one from opengl.org seems to be the newest (it says GL_GLEXT_VERSION 38) but doesn't include declarations for latest nvidia extensions. The one on nvidia's site is GL_GLEXT_VERSION 28, and the one on sgi is GL_GLEXT_VERSION 29, but doesn't even include declarations for OpenGL 2.1.
In the end it seems like the oldest header file by version (the one from nvidia) is most up-to-date.
I guess ati must have its own header file that includes ATI's last additions.
One could say the same about extension registries - all sites seem to have their own, unsync'd with all the others.
Since header file updates must be coordinated in some way I wonder if there exists an integral version of glext.h which includes all of the latest extensions.
Re: glext.h versions
Maybe the one from Mesa ?
nvidia, ati won't provide extensions they don't support, that turns out. It might be the same for sgi. For the one from opengl.org, I guess it gives only generic extensions (the ones that should be supported by all vendors).
Simply use the one from your hardware vendor. But if you need support for all extensions (or from various vendors), it might be a mess. As I stippled above, try to check the one from Mesa...
Or buy another PC with a graphic card from another vendor