Although I don't have vista, take this with a grain of salt since I'm not up to date regarding the matter..
But Vista runs OpenAL, and has removed support for directsound, so there are issues. I'm not sure of the severity, but it's pretty bad, you have to pretty much run a application called Alchemy for soundblaster cards, in order to get decent quality sound and directional hearing.
Once again I don't have vista, so you should listen to someone who has both vista and a soundblaster card to give you the entire picture.