   Making a game run in D3D9 or D3D10
  I've thought about making a game that would run in D3D9 on any Windows before Vista and in D3D10 for Vista or Windows 7, mostly as a way to learn about D3D10.  However, I'm likely not going to be using advanced techniques like shaders, bump mapping, and so on.  For a simple game that would mostly be textured quads and sprites, would it be better (or easier) to just run it in D3D9 on every Windows OS and leave D3D10 out?  Or does D3D10 really have some significant benefits for beginners that D3D9 does not?   
  D3D10 is a much cleaner API then 9. But for your use case 10 would be overkill. Especial as 10 requires doing anything with shaders. Therefore I recommend staying with 9 for this project.   