If you have a sound card based on the Aureal Vortex 1 (AU8820) chip, you should head immediately to Aureal's web site to get the latest A3D drivers. I had always been very disappointed with the 3D sound of my Vortex1 card. It dragged framerates way down, and it didn't sound very '3d' to me. After I installed these latest drivers, however, the situation changed dramatically. Performance was better (although still affected), but the sound depth was tremendous. It was like a whole new card. You need this new driver.
Keep in mind that this is only for the 3D component of your sound card and won't affect the performance of non-A3D accelerated applications.