Good question, so I'll follow up with a stupid one: does the creative card come with any documentation/install instructions? My first instinct is to say go ahead and install the Realtek driver. My reasoning is that since what you have is an "add-in" card, it may assume that there are already audio drivers installed on the system, so installing over any existing ones shouldn't be an issue. But I will defer to someone with more experience with discrete sound cards...