Directx question

Use the latest supported by your OS. DX11 is a super set of DX10, it will run on a DX10 card like your 8800GTX and will use only DX10 instructions so it wont cause any issues.

your gpu is the determining factor on which version of dx you can / you should use. since that 8800gtx only has dx10 support you're stuck with dx10.

DX is primarily determined by your video card and secondarily by your operating system.

Your 8800GTX is a DX10 video card. Your operating system is Windows 7 supports up to DX11. However, you will not be able to take advantage of any DX11 effects because your video card is limited to DX10. There is no "software patch" you can use; you have a physical hardware limitation.

If you were to have your DX10 card in a system that uses Windows XP, then would will be limited to DX9 because Win XP only supports up to DX9. DX10 and DX11 cannot be installed on Win XP. In this scenario, you are limited by software (the OS) and not your video card.