One more step in case you're unaware..

Vista removed all hardware audio support in DirectX 10, therefore making your X-Fi sound card useless.. without help. (Sound card companies are furious I'm sure..)

Download Creative Lab's Audacity software. It basically creates a wrapper for DirectX<->OpenAL so all your audio processing is done on the sound card again instead of being sent to the CPU for work. You can find Audacity on creativelabs.com.