WaveRT Preferences
These are the preference options if WaveRT mode is selected on the Sound Device Preferences.  WaveRT stands for Wave Real Time and is Microsoft's new audio driver layer for Window's Vista only.

Latency
Adjust the number of milliseconds of latency that you'd like.  Lower numbers are better for performance.  However, as you lower the latency, you are also increasing the potential for audio gapping or non-continuous audio.

WaveRT is the preferred driver.  Make sure that you have the latest drivers for your sound device.  Also, contact your sound device manufacturer to see if the audio drivers support WaveRT properly.