Creative Labs sucks, but take a look at this and see if it helps. Creative Labs screwed up royally with their PCI settings.
The problem is "bus mastering". There is a registry setting with the Live! series that helps. I have long since gotten rid of all my SB cards (I use Turtle Beach cards), but I remember the "turbo=0" setting that goes into the registry to disable bus mastering with SB Live! cards.