Can you read how much VRAM the system has?
If so, you can pre-calc how much width x height x bpp will use, double it (for page flipping) and if the video card can't cope with it, then reduce the resolution to something acceptable.
If so, you can pre-calc how much width x height x bpp will use, double it (for page flipping) and if the video card can't cope with it, then reduce the resolution to something acceptable.