Is it possible for me to enable DirectX 7.0?

Is it possible for me to enforce directx 7.0 because i seem to get more fps with that in the game called Call Of Duty 2 Demo, and i think it will boost my fps is Call Of Duty United Offensive too if there is anyway to enforce directx 7.0 instead of the lastest version witch i have right now please tell me how thanks!
:)

Oh yeah only reason why i can enforce it in the CoD2 Demo because it has it in the options.