How to use directx 9 on directx 11

Windows 7 already has all versions of DX. The game, video card, and OS must all support the version of DX that you are trying to use, otherwise it will default to the least common denominator. That is, if your vid card only supports DX9 the game will only use DX9 even if the OS has DX10 and DX11 available to it.
 
What hawkeye said, with one minor addition: Since Vista came out, DX9 has been updated a few times, so a few DX9 .dll files may not be installed by your system. Microsoft has a DX Web Updater which ensures all the DX files are up to date, and I recommend running it if you have any DX errors.
 


I've posted links to both the web installer and the full runtime download, just in case it's needed.

Web Installer:
http://www.microsoft.com/download/en/details.aspx?id=35

Full runtime:
http://www.microsoft.com/download/en/details.aspx?displaylang=en&id=8109