Sorry versions, were a bit rusty in my memory, so I did some more research. So setting it at XP SP3 as your minimum level, would give you DirectX 9.0c, sub-version 4.09.00.0904. SP2 still gives you DirectX 9.0c, just the earlier un-patched version. Probably any of the issues would not effect 2D applications anyway. So I suppose either version would be fine. And reading a lot further down in your change log (than I did originally) I see you already use the DirectX API anyway, so ignore my aimless ramblings. Must be getting senile 
tcruise: we use SDL to access graphics. So whatever SDL does, is what we're using. No idea if that is DirectX. For the SDLGL-PP renderer we use OpenGL 2 via SDL.
There is an option to enable SDL through directx... AFAIK this was big fail.
openMSX is not only for windows but for every platform with GCC and SDL 
