1. Microsoft doesnt come with opengl, doesnt support it or whatever. However it CAN be installed and used with opengl applications. This points us to...
2. Your video card manufacturer. Well most of us here got good cards and some people still play with 3dfx and so forth. All these cards come with software that installs open GL drivers into the System. This excludes them as the problem even though it may seem its your cards fault. Henceforth this leads us to the last suspect which is...
3. Sierra. On my system this is the obvious vagrant causing the problem. Why? Well all my other open gl apps work fine with my card and OS which means they are properly configuered. Sierra needs to get off their ass and release a patch that makes half life and its mods work with XP.