Direct x 9.0c

[Manicoti]

Hello everyone!
Just found this website and what great info it has!! I'll definately be spending time here:)
My question is regarding direct x drivers. I just bought a new comp and i'm not sure which direct x driver it had. When i played Pacific fighters, i was getting high 70's for frames. I also recently installed Call of Duty's expansion pack and it installed Direct X 9.0c. Now i've noticed that i only get around 35 for frames in PF, with no changes to graphic settings etc.
Could this new direct x driver have caused the big hit in frames??
If so, which version of direct x should i instal? And can i instal an older version of direct x over the 9.0c driver?
Thanks for the info!
Mani