If you have a graphics card of a well-known brand (nVidia, ATI, Matrox...), well you're stuck because these cards are undocumented (though I heard that ATI was now managed by AMD and the specifications were being opened, but don't know at all if it's true). The problem is that the Windows drivers are coded by the companies themselves (because otherwise, they couldn't sell their silicon) and are closed-source. So if you want to code a graphics driver for these cards, then you'll have a hard time doing that, if you succeed at all. So as an alternative, if VGA, VESA and all documented stuff doesn't give you what you want, I suggest that you consider supporting Intel and AMD graphics cards shipped with modern CPUs (which have reasonnably good resolutions).
I've planned to contact nVidia when I'll get to implementing my GUI to ask if there is documentation available (either for free or not), but I'm still very far from it so you can either do that yourself, or just wait
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