At the risk of oversimplifying 3D sound in Vista; the vendor extensions that allowed the Creative hardware to accelerate 3D sound calculations was removed from the DirectX libraries. If the program uses the 3D audio routines from DirectX it will be calculated on the host CPU even if something like the Creative X-Fi is present. Programs based on OpenAL are not effected by this, and will happily use the Creative hardware.

Creative has written a program to reintroduce hardware acceleration of 3D sound into specific DirectX programs called ALchemy (see http://www.soundblaster.com/alchemy/). World of Warcraft is listed.