DirectX9 will work fine with a DirectX8 card
its backwards compatible.
even using a DirectX8 card,some games will ask you to install version 9 for them to work now.
version 9a has some problems as a lot of its make up files are beta.
9b click here is final release and should give less hastle,its also the redist version which means you just download it like any other download then click on it to install.
ps make sure your graphics card drivers are up to date also.