What do you do to get directx 9.0?

i want to play the sims 2 game but when i try to instal them and i go to run it a message comes up saying failed to find directx 9.0...blah ect. i tried downloading Windows Genuine Advantage validation plug-in installer but it still didnt work. I also tried putting a -w after the description thing or somthing like tht but it didnt work either. please helppp.