I use a Nvidia Geforce 6150SE nforce 430. I looked it up and it says its made for DirectX 9. I use Windows 7 and it came with DirectX 11. So can I install DX9 so i can get the full benefit of the 6150SE when playing games?
You will not need to install anything, Windows 7 is fully compatible with all previous versions of Direct X. The only difference between 9, 10 and 11 is added features, which your card simply will not be able to use, but it will work perfectly fine.