Computer Newb

H i recently installed beta 2 build 5384 and everything seems to be running smooth rxcept i can't get DirectX to work. My game needs 9.0b or better and i have 9.0c on vista now atm i think but when i start the game up i keep getting error saying i do not have DirectX installed etc. so if someone could help that would b great, i can also post a pic of it if i need to.