Okay first off. DX10 cant be removed. @nd do you have a DX10 card? Like a nVidia 8800, 8600 or something like that? If not then this would not affect you at all. Only cards that are DX10 can even render it. So if you dont have a DX10 card you have ntohing to worry about.
As for the DX9 situation...there is no DX9L. They only went as high as DX9c. But to help with you gaming in Vista what you install is hte Runtime.
Download details: DirectX End-User Runtime
Updated as of June. You can install this and not overwrite your DX10 in Vista and play your DX9 games jsut fine.